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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: | |
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| All these are from the [http://www.student.northpark.edu/pemente/sed/sed1line.txt sed one-liners page]: | *Unix systems use Line Feeds (LFs) 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 simply look at the output of `sed -n l`: |
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| 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$//' dosfile # GNUism - does not work with Unix sed! |
sed -n l yourscript |
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| If you want to remove all CRs regardless of whether they are at the end of a line, you can use {{{tr}}}: | If you see something like this, then you're dealing with CRLF style newlines: |
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| tr -d '\r' < dosfile | command\r$ \r$ another command\r$ |
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| If you want to use the second {{{sed}}} example above, but without embedding a literal CR into your script: | Another method is to use the `file` utility if available to guess at the file type: |
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| sed $'s/\r$//' dosfile # BASH only | file yourscript |
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| 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. | 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". |
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| There are many more ways: * Some systems have a {{{dos2unix}}} command which can do this. Or {{{recode}}}, or {{{fromdos}}}. * In {{{vim}}}, you can use {{{:set fileformat=unix}}} to do it. * 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. |
{{{ 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 by a DOS utility, there should be no bare LFs not preceded by a CR. {{{ # 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 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 }}} Of course, Any of the more powerful dynamic languages to 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 these 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 characters (CRs) are used in line ending markers on some systems. There are three different kinds of line endings in common use:
- Unix systems use Line Feeds (LFs) 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 simply look at the output of sed -n l:
sed -n l yourscript
If you see something like this, then you're dealing with CRLF style newlines:
command\r$ \r$ another command\r$
Another method is to use the file utility if available to guess at the file type:
file yourscript
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".
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 by a DOS utility, there should be no bare LFs not preceded by a CR.
# 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 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
Of course, Any of the more powerful dynamic languages to 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 these are not the same file.