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← Revision 29 as of 2022-01-30 01:59:53 ⇥
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| Carriage return characters (CRs) are used in line ending markers on some systems. There are three different kinds of line endings in common use: | Carriage return (CR) characters are used in line ending markers on some systems. There are three different kinds of line endings in common use: |
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| *Unix systems use Line Feeds (LFs) only. | *Unix systems use line feed (LF) characters only. |
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| If you're running a script on a Unix system, the line endings need to be Unix ones (LFs only), or you will have problems. You can check the kind of line endings in use by running: | If you're running a script on a Unix system, the line endings need to be Unix ones (LFs only), or you will have problems. === Testing for line terminator type === A simple check is to look at the output of `sed -n l`: |
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| cat -e yourscript | sed -n l yourscript |
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| If you see something like this: {{{ command^M$ ^M$ another command^M$ }}} |
This should output the script in one of these formats: |
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| then you need to remove the CRs. There are a plethora of ways to do this. | || '''LF (Unix)''' || '''CR-LF (DOS/Windows)''' || '''CR (Old Mac OS)''' || ||<style="border-bottom:none;"> command$ ||<style="border-bottom:none;"> command\r$ ||<style="border-bottom:none;"> command\r\ranother command\r$ || ||<style="border-top:none; border-bottom:none"> $ ||<style="border-top:none; border-bottom:none;"> \r$ ||<style="border-top:none; border-bottom:none;"> || ||<style="border-top:none;"> another command$ ||<style="border-top:none;"> another command\r$ ||<style="border-top:none;"> || |
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| All these are from the [[http://www.student.northpark.edu/pemente/sed/sed1line.txt|sed one-liners page]]: {{{ sed 's/.$//' dosfile # assumes that all lines end with CR/LF sed 's/^M$//' dosfile # in bash/tcsh, press Ctrl-V then Ctrl-M sed 's/\x0D$//' dosfile # GNUism - does not work with Unix sed! }}} |
Another method is to guess at the file type using the `file` utility, if available: |
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| If you want to remove all CRs regardless of whether they are at the end of a line, you can use {{{tr}}}: {{{ tr -d '\r' < dosfile }}} If you want to use the second {{{sed}}} example above, but without embedding a literal CR into your script: {{{ sed $'s/\r$//' dosfile # BASH only }}} All of the previous examples write the modified file to standard output. Redirect the output to a new file, and then {{{mv}}} it over top of the original. There are many more ways: * Some systems have a {{{dos2unix}}} command which can do this. Or {{{recode}}}, or {{{fromdos}}}. * You can also use col <input.txt > output.txt * In {{{vim}}}, you can use {{{:set fileformat=unix}}} to do it and save it with a ":w". * You can use Perl: {{{ perl -pi -e 's/\r\n/\n/' filename }}} This has the advantage of overwriting the original file, so you don't have to mess with temporary files. ---- Another way to check it: |
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| The output tells you whether the ASCII text has some CR, if that's the case. Note: this is only true on GNU/Linux. On other operating systems, the result of `file` is unpredictable, except that it should contain the word "text" somewhere in the output if the result "kind of looks like a text file of some sort, maybe". | On GNU/Linux, the output of `file` tells you whether the ASCII text has some CR. On other operating systems, the output is unpredictable, except that it should contain the word "text" somewhere if the input "kind of looks like a text file of some sort, maybe". |
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| And another way to fix it: | In a script, it's more difficult to say what the most reliable method should be. Anything you do is going to be a heuristic. In theory, a non-corrupt file created by a non-broken UNIX utility should only contain LFs, and one created by a DOS utility should not contain any LFs that are not preceded by a CR. {{{#!highlight bash # Bash / Ksh / Zsh if grep -qv $'\r$' File; then echo 'File contains at least one newline not preceded by a CR' else echo 'File contains only CRLFs (or is empty)' fi }}} === Converting files === `ex` is a good standard way to convert CRLF to LF, and probably one of the few reasonable methods for doing it [[BashFAQ/021#Files|in-place]] from a script: {{{#!highlight bash numbers=disable # works with vim's ex but not vi's ex ex -sc $'%s/\r$//e|x' file # works with vi's ex but not vim's ex ex -sc $'%s/\r$//|x' file }}} {{{#!highlight bash numbers=disable # Using ed. ed -s file <<< $'%s/\r$//g\nwq' }}} Of course, more powerful dynamic languages can do this with relative ease. {{{ perl -pi -e 's/\r\n/\n/' filename }}} Some systems have special conversion tools available to do this automatically. `dos2unix`, `recode`, and `fromdos` are some examples. It be done manually with an editor like nano: |
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Or in Vim, use `:set fileformat=unix` and save with `:w`. Ensure the value of `fenc` is correct (probably "utf-8"). To simply strip all CRs from some input stream, you can use `tr -d '\r' <infile >outfile`. Of course, you must ensure that `infile` and `outfile` [[BashPitfalls#pf13|are not the same file]]. |
How do I convert a file from DOS format to UNIX format (remove CRs from CR-LF line terminators)?
Carriage return (CR) characters are used in line ending markers on some systems. There are three different kinds of line endings in common use:
- Unix systems use line feed (LF) characters only.
- MS-DOS and Windows systems use CR-LF pairs.
- Old Macintosh systems use CRs only.
If you're running a script on a Unix system, the line endings need to be Unix ones (LFs only), or you will have problems.
Testing for line terminator type
A simple check is to look at the output of sed -n l:
sed -n l yourscript
This should output the script in one of these formats:
LF (Unix) |
CR-LF (DOS/Windows) |
CR (Old Mac OS) |
command$ |
command\r$ |
command\r\ranother command\r$ |
$ |
\r$ |
|
another command$ |
another command\r$ |
|
Another method is to guess at the file type using the file utility, if available:
file yourscript
On GNU/Linux, the output of file tells you whether the ASCII text has some CR. On other operating systems, the output is unpredictable, except that it should contain the word "text" somewhere if the input "kind of looks like a text file of some sort, maybe".
imadev:~$ printf 'DOS\r\nline endings\r\n' > foo imadev:~$ file foo foo: commands text arc3:~$ file foo foo: ASCII text, with CRLF line terminators
In a script, it's more difficult to say what the most reliable method should be. Anything you do is going to be a heuristic. In theory, a non-corrupt file created by a non-broken UNIX utility should only contain LFs, and one created by a DOS utility should not contain any LFs that are not preceded by a CR.
Converting files
ex is a good standard way to convert CRLF to LF, and probably one of the few reasonable methods for doing it in-place from a script:
# works with vim's ex but not vi's ex
ex -sc $'%s/\r$//e|x' file
# works with vi's ex but not vim's ex
ex -sc $'%s/\r$//|x' file
# Using ed.
ed -s file <<< $'%s/\r$//g\nwq'
Of course, more powerful dynamic languages can do this with relative ease.
perl -pi -e 's/\r\n/\n/' filename
Some systems have special conversion tools available to do this automatically. dos2unix, recode, and fromdos are some examples.
It be done manually with an editor like nano:
nano -w yourscript
Type Ctrl-O and before confirming, type Alt-D (DOS) or Alt-M (Mac) to change the format.
Or in Vim, use :set fileformat=unix and save with :w. Ensure the value of fenc is correct (probably "utf-8").
To simply strip all CRs from some input stream, you can use tr -d '\r' <infile >outfile. Of course, you must ensure that infile and outfile are not the same file.