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Best practice to use $? in bash?

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.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

10

10

When I read this answer about $? another question comes to mind.

Is there any best practice for how to use $? in bash?

---

Let's have a example:

We have a linear script and I we would like to know that all the command was executed ok.
Do you think it is ok to call a small function (let's call it "did_it_work"),
to check the error code and break if it's not.

#!/bin/bash 



function did_it_work {

    code=$1

    if [ "$code" -ne "0" ]

    then

        echo "Error failure: code $code "

        exit 1

    fi

}



dir=some/path



mkdir -p $dir

did_it_work $? 



cd $dir

did_it_work $? 



run_some_command

did_it_work $? 

This approach of course means that I have to manually solve the problem if there is any and rerun the script.

Do you think this is a good idea or is there some other best practice to do this?

/Thanks

shell bash error-handling

share|improve this question

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

add a comment | 

10

10

When I read this answer about $? another question comes to mind.

Is there any best practice for how to use $? in bash?

---

Let's have a example:

We have a linear script and I we would like to know that all the command was executed ok.
Do you think it is ok to call a small function (let's call it "did_it_work"),
to check the error code and break if it's not.

#!/bin/bash 



function did_it_work {

    code=$1

    if [ "$code" -ne "0" ]

    then

        echo "Error failure: code $code "

        exit 1

    fi

}



dir=some/path



mkdir -p $dir

did_it_work $? 



cd $dir

did_it_work $? 



run_some_command

did_it_work $? 

This approach of course means that I have to manually solve the problem if there is any and rerun the script.

Do you think this is a good idea or is there some other best practice to do this?

/Thanks

shell bash error-handling

share|improve this question

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

add a comment | 

When I read this answer about $? another question comes to mind.

Is there any best practice for how to use $? in bash?

---

Let's have a example:

We have a linear script and I we would like to know that all the command was executed ok.
Do you think it is ok to call a small function (let's call it "did_it_work"),
to check the error code and break if it's not.

#!/bin/bash 



function did_it_work {

    code=$1

    if [ "$code" -ne "0" ]

    then

        echo "Error failure: code $code "

        exit 1

    fi

}



dir=some/path



mkdir -p $dir

did_it_work $? 



cd $dir

did_it_work $? 



run_some_command

did_it_work $? 

This approach of course means that I have to manually solve the problem if there is any and rerun the script.

Do you think this is a good idea or is there some other best practice to do this?

/Thanks

shell bash error-handling

share|improve this question

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

#!/bin/bash 



function did_it_work {

    code=$1

    if [ "$code" -ne "0" ]

    then

        echo "Error failure: code $code "

        exit 1

    fi

}



dir=some/path



mkdir -p $dir

did_it_work $? 



cd $dir

did_it_work $? 



run_some_command

did_it_work $? 

share|improve this question

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

share|improve this question

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

edited Apr 13 '17 at 12:36

Community♦

1

edited Apr 13 '17 at 12:36

Community♦

1

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

asked Mar 7 '11 at 16:35

JohanJohan

3,38911830

3 Answers
3

active

oldest

votes

14

One common way is:

die() {

    echo "$*" 1>&2

    exit 1

}

then you use it like this:

mkdir -p some/path || die "mkdir failed with status $?"

Or if you want it to include the exit status, you could change it to:

die() {

    echo "FATAL ERROR: $* (status $?)" 1>&2

    exit 1

}

and then using it is a bit easier:

mkdir -p some/path || die "mkdir failed"

Just in case you haven't seen command1 || command2 before, it runs command1, and if command1 fails, it runs command2.

So you can read it like "make the directory or die".

Your example would look like:

mkdir -p some/path || die "mkdir failed"

cd some/path || die "cd failed"

run_some_command || die "some_command failed"

Or you can align the dies further on the right so that the main code is more obvious.

mkdir -p some/path         || die "mkdir failed"

cd some/path               || die "cd failed"

run_some_command           || die "some_command failed"

---

Also, if you are going to use the name some/path multiple times, store it in a variable so you don't have to keep typing it, and can easily change it if you need to.

dir=some/path

mkdir -p "$dir"            || die "Cannot make $dir"

cd "$dir"                  || die "Cannot cd to $dir"

run_some_command           || die "Cannot run some_command"

share|improve this answer

edited 10 mins ago

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

add a comment | 

8

You could rewrite your code like this:

#!/bin/bash

function try {

    "$@"

    code=$?

    if [ $code -ne 0 ]

    then

        echo "$1 did not work: exit status $code"

        exit 1

    fi

}



try mkdir -p some/path

try cd some/path

try run_some_command

If you don't actually need to log the error code, but just whether the command succeeded or not, you can shorten try() further like so:

function try {

    if ! "$@"

    then

        echo "$1 did not work"

        exit 1

    fi

}

share|improve this answer

edited Mar 7 '11 at 20:12

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can also use the code in this format. <pre>function try {
  
  – BillThor
  Mar 7 '11 at 17:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you use this functionality inline and don't want to return from the true side you can replace return $? with the : builtin.
  
  – BillThor
  Mar 7 '11 at 17:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why give a version that doesn't work with spaces? Change $* to "$@".
  
  – Mikel
  Mar 7 '11 at 19:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've fixed it for you.
  
  – Mikel
  Mar 7 '11 at 20:05
  

  
  
  
  

add a comment | 

7

If you really want to exit on an error and are using Bash, then you should also consider set -e. From help set:

-e Exit immediately if a command exits with a non-zero status.

This of course doesn't give you the flexibility of a did_it_work() function, but it is an easy way to make sure your bash script stops on an error without adding lots of calls to your new function.

share|improve this answer

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  set -e is useful. There are some commands that return non-zero under normal circumstances (for instance, diff). When I'm using set -e in a script where I'm expecting a nonzero return, I do command || true.
  
  – Shawn J. Goff
  Mar 7 '11 at 18:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Furthermore, even if you use set -e, you can set an “exception handler” to catch all errors with trap did_it_work EXIT.
  
  – Gilles
  Mar 8 '11 at 18:41
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is part of POSIX, not a bash specific feature. Use it but be aware of some pitfalls mywiki.wooledge.org/BashFAQ/105
  
  – kmkaplan
  Feb 5 '14 at 7:46
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ShawnJ.Goff I prefer to do command && true. Like that the return value is not changed.
  
  – kmkaplan
  Feb 5 '14 at 7:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @kmkaplan Your last comment doesn't make any sense to me. The purpose of command || true is to prevent set -e from exiting the script if command returns a non-zero exit code. It changes the exit code because we need to. The only thing command && true does is run true (return a zero exit code) if `command succeeded (returned a zero exit code) - it's a complete no-op.
  
  – tripleee
  yesterday
  

  
  
  
  

add a comment | 

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14

One common way is:

die() {

    echo "$*" 1>&2

    exit 1

}

then you use it like this:

mkdir -p some/path || die "mkdir failed with status $?"

Or if you want it to include the exit status, you could change it to:

die() {

    echo "FATAL ERROR: $* (status $?)" 1>&2

    exit 1

}

and then using it is a bit easier:

mkdir -p some/path || die "mkdir failed"

Just in case you haven't seen command1 || command2 before, it runs command1, and if command1 fails, it runs command2.

So you can read it like "make the directory or die".

Your example would look like:

mkdir -p some/path || die "mkdir failed"

cd some/path || die "cd failed"

run_some_command || die "some_command failed"

Or you can align the dies further on the right so that the main code is more obvious.

mkdir -p some/path         || die "mkdir failed"

cd some/path               || die "cd failed"

run_some_command           || die "some_command failed"

---

Also, if you are going to use the name some/path multiple times, store it in a variable so you don't have to keep typing it, and can easily change it if you need to.

dir=some/path

mkdir -p "$dir"            || die "Cannot make $dir"

cd "$dir"                  || die "Cannot cd to $dir"

run_some_command           || die "Cannot run some_command"

share|improve this answer

edited 10 mins ago

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

add a comment | 

14

One common way is:

die() {

    echo "$*" 1>&2

    exit 1

}

then you use it like this:

mkdir -p some/path || die "mkdir failed with status $?"

Or if you want it to include the exit status, you could change it to:

die() {

    echo "FATAL ERROR: $* (status $?)" 1>&2

    exit 1

}

and then using it is a bit easier:

mkdir -p some/path || die "mkdir failed"

Just in case you haven't seen command1 || command2 before, it runs command1, and if command1 fails, it runs command2.

So you can read it like "make the directory or die".

Your example would look like:

mkdir -p some/path || die "mkdir failed"

cd some/path || die "cd failed"

run_some_command || die "some_command failed"

Or you can align the dies further on the right so that the main code is more obvious.

mkdir -p some/path         || die "mkdir failed"

cd some/path               || die "cd failed"

run_some_command           || die "some_command failed"

---

Also, if you are going to use the name some/path multiple times, store it in a variable so you don't have to keep typing it, and can easily change it if you need to.

dir=some/path

mkdir -p "$dir"            || die "Cannot make $dir"

cd "$dir"                  || die "Cannot cd to $dir"

run_some_command           || die "Cannot run some_command"

share|improve this answer

edited 10 mins ago

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

add a comment | 

One common way is:

die() {

    echo "$*" 1>&2

    exit 1

}

then you use it like this:

mkdir -p some/path || die "mkdir failed with status $?"

Or if you want it to include the exit status, you could change it to:

die() {

    echo "FATAL ERROR: $* (status $?)" 1>&2

    exit 1

}

and then using it is a bit easier:

mkdir -p some/path || die "mkdir failed"

Just in case you haven't seen command1 || command2 before, it runs command1, and if command1 fails, it runs command2.

So you can read it like "make the directory or die".

Your example would look like:

mkdir -p some/path || die "mkdir failed"

cd some/path || die "cd failed"

run_some_command || die "some_command failed"

Or you can align the dies further on the right so that the main code is more obvious.

mkdir -p some/path         || die "mkdir failed"

cd some/path               || die "cd failed"

run_some_command           || die "some_command failed"

---

Also, if you are going to use the name some/path multiple times, store it in a variable so you don't have to keep typing it, and can easily change it if you need to.

dir=some/path

mkdir -p "$dir"            || die "Cannot make $dir"

cd "$dir"                  || die "Cannot cd to $dir"

run_some_command           || die "Cannot run some_command"

share|improve this answer

edited 10 mins ago

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

die() {

    echo "$*" 1>&2

    exit 1

}

mkdir -p some/path || die "mkdir failed with status $?"

die() {

    echo "FATAL ERROR: $* (status $?)" 1>&2

    exit 1

}

mkdir -p some/path || die "mkdir failed"

mkdir -p some/path || die "mkdir failed"

cd some/path || die "cd failed"

run_some_command || die "some_command failed"

mkdir -p some/path         || die "mkdir failed"

cd some/path               || die "cd failed"

run_some_command           || die "some_command failed"

dir=some/path

mkdir -p "$dir"            || die "Cannot make $dir"

cd "$dir"                  || die "Cannot cd to $dir"

run_some_command           || die "Cannot run some_command"

share|improve this answer

edited 10 mins ago

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

answered Mar 7 '11 at 19:54

MikelMikel

41.1k10103128

8

You could rewrite your code like this:

#!/bin/bash

function try {

    "$@"

    code=$?

    if [ $code -ne 0 ]

    then

        echo "$1 did not work: exit status $code"

        exit 1

    fi

}



try mkdir -p some/path

try cd some/path

try run_some_command

If you don't actually need to log the error code, but just whether the command succeeded or not, you can shorten try() further like so:

function try {

    if ! "$@"

    then

        echo "$1 did not work"

        exit 1

    fi

}

share|improve this answer

edited Mar 7 '11 at 20:12

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can also use the code in this format. <pre>function try {
  
  – BillThor
  Mar 7 '11 at 17:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you use this functionality inline and don't want to return from the true side you can replace return $? with the : builtin.
  
  – BillThor
  Mar 7 '11 at 17:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why give a version that doesn't work with spaces? Change $* to "$@".
  
  – Mikel
  Mar 7 '11 at 19:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've fixed it for you.
  
  – Mikel
  Mar 7 '11 at 20:05
  

  
  
  
  

add a comment | 

8

You could rewrite your code like this:

#!/bin/bash

function try {

    "$@"

    code=$?

    if [ $code -ne 0 ]

    then

        echo "$1 did not work: exit status $code"

        exit 1

    fi

}



try mkdir -p some/path

try cd some/path

try run_some_command

If you don't actually need to log the error code, but just whether the command succeeded or not, you can shorten try() further like so:

function try {

    if ! "$@"

    then

        echo "$1 did not work"

        exit 1

    fi

}

share|improve this answer

edited Mar 7 '11 at 20:12

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can also use the code in this format. <pre>function try {
  
  – BillThor
  Mar 7 '11 at 17:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you use this functionality inline and don't want to return from the true side you can replace return $? with the : builtin.
  
  – BillThor
  Mar 7 '11 at 17:50
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why give a version that doesn't work with spaces? Change $* to "$@".
  
  – Mikel
  Mar 7 '11 at 19:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've fixed it for you.
  
  – Mikel
  Mar 7 '11 at 20:05
  

  
  
  
  

add a comment | 

You could rewrite your code like this:

#!/bin/bash

function try {

    "$@"

    code=$?

    if [ $code -ne 0 ]

    then

        echo "$1 did not work: exit status $code"

        exit 1

    fi

}



try mkdir -p some/path

try cd some/path

try run_some_command

If you don't actually need to log the error code, but just whether the command succeeded or not, you can shorten try() further like so:

function try {

    if ! "$@"

    then

        echo "$1 did not work"

        exit 1

    fi

}

share|improve this answer

edited Mar 7 '11 at 20:12

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

#!/bin/bash

function try {

    "$@"

    code=$?

    if [ $code -ne 0 ]

    then

        echo "$1 did not work: exit status $code"

        exit 1

    fi

}



try mkdir -p some/path

try cd some/path

try run_some_command

function try {

    if ! "$@"

    then

        echo "$1 did not work"

        exit 1

    fi

}

share|improve this answer

edited Mar 7 '11 at 20:12

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

answered Mar 7 '11 at 16:47

Warren YoungWarren Young

57.1k11145150

7

If you really want to exit on an error and are using Bash, then you should also consider set -e. From help set:

-e Exit immediately if a command exits with a non-zero status.

This of course doesn't give you the flexibility of a did_it_work() function, but it is an easy way to make sure your bash script stops on an error without adding lots of calls to your new function.

share|improve this answer

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  set -e is useful. There are some commands that return non-zero under normal circumstances (for instance, diff). When I'm using set -e in a script where I'm expecting a nonzero return, I do command || true.
  
  – Shawn J. Goff
  Mar 7 '11 at 18:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Furthermore, even if you use set -e, you can set an “exception handler” to catch all errors with trap did_it_work EXIT.
  
  – Gilles
  Mar 8 '11 at 18:41
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  This is part of POSIX, not a bash specific feature. Use it but be aware of some pitfalls mywiki.wooledge.org/BashFAQ/105
  
  – kmkaplan
  Feb 5 '14 at 7:46
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @ShawnJ.Goff I prefer to do command && true. Like that the return value is not changed.
  
  – kmkaplan
  Feb 5 '14 at 7:49
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @kmkaplan Your last comment doesn't make any sense to me. The purpose of command || true is to prevent set -e from exiting the script if command returns a non-zero exit code. It changes the exit code because we need to. The only thing command && true does is run true (return a zero exit code) if `command succeeded (returned a zero exit code) - it's a complete no-op.
  
  – tripleee
  yesterday
  

  
  
  
  

add a comment | 

7

If you really want to exit on an error and are using Bash, then you should also consider set -e. From help set:

-e Exit immediately if a command exits with a non-zero status.

This of course doesn't give you the flexibility of a did_it_work() function, but it is an easy way to make sure your bash script stops on an error without adding lots of calls to your new function.

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answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

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  set -e is useful. There are some commands that return non-zero under normal circumstances (for instance, diff). When I'm using set -e in a script where I'm expecting a nonzero return, I do command || true.
  
  – Shawn J. Goff
  Mar 7 '11 at 18:49
  

  
  
  
  


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  Furthermore, even if you use set -e, you can set an “exception handler” to catch all errors with trap did_it_work EXIT.
  
  – Gilles
  Mar 8 '11 at 18:41
  

  
  
  
  


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  This is part of POSIX, not a bash specific feature. Use it but be aware of some pitfalls mywiki.wooledge.org/BashFAQ/105
  
  – kmkaplan
  Feb 5 '14 at 7:46
  
  
  

  
  
  
  


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  @ShawnJ.Goff I prefer to do command && true. Like that the return value is not changed.
  
  – kmkaplan
  Feb 5 '14 at 7:49
  

  
  
  
  


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  @kmkaplan Your last comment doesn't make any sense to me. The purpose of command || true is to prevent set -e from exiting the script if command returns a non-zero exit code. It changes the exit code because we need to. The only thing command && true does is run true (return a zero exit code) if `command succeeded (returned a zero exit code) - it's a complete no-op.
  
  – tripleee
  yesterday
  

  
  
  
  

add a comment | 

If you really want to exit on an error and are using Bash, then you should also consider set -e. From help set:

-e Exit immediately if a command exits with a non-zero status.

This of course doesn't give you the flexibility of a did_it_work() function, but it is an easy way to make sure your bash script stops on an error without adding lots of calls to your new function.

share|improve this answer

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

share|improve this answer

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108

answered Mar 7 '11 at 18:14

Steven DSteven D

33.6k899108