Mdthbs

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What is the meaning of read -r ?

Why is `while IFS= read` used so often, instead of `IFS=; while read..`?How to read input lines with newline characters from command line?What is the meaning of the .: in this linux statement?In what shared library is read()?What is the meaning of ls -d ?How does “-dc” work in “cat /dev/urandom | tr -dc ”01"?What does the -p option do in the read command?What is the FreeBSD equivalent of “read -n”?read value validationWhat does `while read -r line || [[ -n $line ]]` mean?BASH question: using read, can I capture a single char OR arrow key (on keyup)Why bash “read -t 0” does not see input?

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

19

6

in order to understand another answer:

find / -type d -print0 | while read -r -d ''; do ls -ltr "$dir" | sed '$!d'

the first step is to understand the usage of the option -r of the read command.

First, I thought, it would be sufficient to simply execute

man read

to lookup the meaning of the -r option ,
but I realized the man page does not contain any explanation for option at all,
so I googled for it got some read -t , read -p examples but no read -r .

command-line read

share|improve this question

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Are you saying there's no man page for read ? If I type man read I get a long list of Bash built in commands. I searched using '/read' I've put what I saw here pastebin.com/raw.php?i=tZ1uUXrG
  
  – user610209
  Mar 27 '15 at 0:51
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It's a shell built in (at least in bash) - try help read or man bash
  
  – steeldriver
  Mar 27 '15 at 0:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Regarding your title question, read unix.stackexchange.com/questions/18886/…
  
  – Gilles
  Mar 27 '15 at 1:02
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  READ(1P) exists for me...
  
  – jasonwryan
  Mar 27 '15 at 1:06
  

  
  
  
  

add a comment | 

19

6

in order to understand another answer:

find / -type d -print0 | while read -r -d ''; do ls -ltr "$dir" | sed '$!d'

the first step is to understand the usage of the option -r of the read command.

First, I thought, it would be sufficient to simply execute

man read

to lookup the meaning of the -r option ,
but I realized the man page does not contain any explanation for option at all,
so I googled for it got some read -t , read -p examples but no read -r .

command-line read

share|improve this question

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Are you saying there's no man page for read ? If I type man read I get a long list of Bash built in commands. I searched using '/read' I've put what I saw here pastebin.com/raw.php?i=tZ1uUXrG
  
  – user610209
  Mar 27 '15 at 0:51
  
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It's a shell built in (at least in bash) - try help read or man bash
  
  – steeldriver
  Mar 27 '15 at 0:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Regarding your title question, read unix.stackexchange.com/questions/18886/…
  
  – Gilles
  Mar 27 '15 at 1:02
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  READ(1P) exists for me...
  
  – jasonwryan
  Mar 27 '15 at 1:06
  

  
  
  
  

add a comment | 

in order to understand another answer:

find / -type d -print0 | while read -r -d ''; do ls -ltr "$dir" | sed '$!d'

the first step is to understand the usage of the option -r of the read command.

First, I thought, it would be sufficient to simply execute

man read

to lookup the meaning of the -r option ,
but I realized the man page does not contain any explanation for option at all,
so I googled for it got some read -t , read -p examples but no read -r .

command-line read

share|improve this question

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

find / -type d -print0 | while read -r -d ''; do ls -ltr "$dir" | sed '$!d'

man read

share|improve this question

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

share|improve this question

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

asked Mar 27 '15 at 0:43

Abdul Al HazredAbdul Al Hazred

8,0672121 gold badges4444 silver badges7373 bronze badges

2 Answers
2

active

oldest

votes

24

There is no stand-alone read command: instead, it is a shell built-in, and as such is documented in the man page for bash:

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p

prompt] [-t timeout] [-u fd] [name ...]

[...]

       -r     Backslash does not act as an escape character.  The back‐

              slash is considered to be part of the line.  In  particu‐

              lar,  a  backslash-newline pair may not be used as a line

              continuation.

So, to summarize, read normally allows long lines to be broken using a trailing backslash character, and normally reconstructs such lines. This slightly surprising behavior can be deactivated using -r.

share|improve this answer

edited Mar 27 '15 at 1:00

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  A demo: str="abc"; read x <<< "$str"; read -r y <<< "$str"; echo "$x"; echo "$y"
  
  – glenn jackman
  Mar 27 '15 at 12:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @glennjackman That's great, it's even more striking if you type str="a` and then hit Enter before pasting in the rest of the command starting with b`.
  
  – ErikE
  Jun 20 '18 at 16:52
  

  
  
  
  

add a comment | 

0

The -r option prevents backslash escapes from being interpreted. Here's an example:

Assume there's a file with this content:

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMsNi3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read -r line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

share|improve this answer

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

add a comment | 

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24

There is no stand-alone read command: instead, it is a shell built-in, and as such is documented in the man page for bash:

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p

prompt] [-t timeout] [-u fd] [name ...]

[...]

       -r     Backslash does not act as an escape character.  The back‐

              slash is considered to be part of the line.  In  particu‐

              lar,  a  backslash-newline pair may not be used as a line

              continuation.

So, to summarize, read normally allows long lines to be broken using a trailing backslash character, and normally reconstructs such lines. This slightly surprising behavior can be deactivated using -r.

share|improve this answer

edited Mar 27 '15 at 1:00

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  A demo: str="abc"; read x <<< "$str"; read -r y <<< "$str"; echo "$x"; echo "$y"
  
  – glenn jackman
  Mar 27 '15 at 12:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @glennjackman That's great, it's even more striking if you type str="a` and then hit Enter before pasting in the rest of the command starting with b`.
  
  – ErikE
  Jun 20 '18 at 16:52
  

  
  
  
  

add a comment | 

24

There is no stand-alone read command: instead, it is a shell built-in, and as such is documented in the man page for bash:

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p

prompt] [-t timeout] [-u fd] [name ...]

[...]

       -r     Backslash does not act as an escape character.  The back‐

              slash is considered to be part of the line.  In  particu‐

              lar,  a  backslash-newline pair may not be used as a line

              continuation.

So, to summarize, read normally allows long lines to be broken using a trailing backslash character, and normally reconstructs such lines. This slightly surprising behavior can be deactivated using -r.

share|improve this answer

edited Mar 27 '15 at 1:00

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

• 
  
  
  

  
  9
  

  
  
  
  
  
  

  
  
  A demo: str="abc"; read x <<< "$str"; read -r y <<< "$str"; echo "$x"; echo "$y"
  
  – glenn jackman
  Mar 27 '15 at 12:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @glennjackman That's great, it's even more striking if you type str="a` and then hit Enter before pasting in the rest of the command starting with b`.
  
  – ErikE
  Jun 20 '18 at 16:52
  

  
  
  
  

add a comment | 

There is no stand-alone read command: instead, it is a shell built-in, and as such is documented in the man page for bash:

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p

prompt] [-t timeout] [-u fd] [name ...]

[...]

       -r     Backslash does not act as an escape character.  The back‐

              slash is considered to be part of the line.  In  particu‐

              lar,  a  backslash-newline pair may not be used as a line

              continuation.

So, to summarize, read normally allows long lines to be broken using a trailing backslash character, and normally reconstructs such lines. This slightly surprising behavior can be deactivated using -r.

share|improve this answer

edited Mar 27 '15 at 1:00

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p

prompt] [-t timeout] [-u fd] [name ...]

[...]

       -r     Backslash does not act as an escape character.  The back‐

              slash is considered to be part of the line.  In  particu‐

              lar,  a  backslash-newline pair may not be used as a line

              continuation.

share|improve this answer

edited Mar 27 '15 at 1:00

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

answered Mar 27 '15 at 0:53

dhagdhag

11.8k33 gold badges3434 silver badges4747 bronze badges

0

The -r option prevents backslash escapes from being interpreted. Here's an example:

Assume there's a file with this content:

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMsNi3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read -r line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

share|improve this answer

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

add a comment | 

0

The -r option prevents backslash escapes from being interpreted. Here's an example:

Assume there's a file with this content:

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMsNi3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read -r line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

share|improve this answer

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

add a comment | 

The -r option prevents backslash escapes from being interpreted. Here's an example:

Assume there's a file with this content:

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMsNi3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read -r line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

share|improve this answer

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMsNi3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

$ while read -r line; do echo $line; done < tempfile

ngRTM6hNqgziZcqCcEJN7bHAP9a1GeMs

Ni3EAX1qvogWpRIPE3oagJL6nwlQQW9y

bjJHyaVBrUcyZOY5U4h9QHnpEPqg\\\\Q9Fk

iNOvAyBTAcN5n1uwR4GvRfAGUbPWiXaxn

cqGPPStH3gaWolrfVAlMtoWiSuLa7GzQnnn

EnO04N1nEkpWbfXRxrtYNqCZDpFtrQIXS

share|improve this answer

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

edited 26 mins ago

muru

41.5k55 gold badges101101 silver badges175175 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges

answered 3 hours ago

aderchoxaderchox

1577 bronze badges