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This article is a cheat sheet for things you learn to do in Bash (The Bourne Again Shell).
== For Loops ==
The bash one-liner for doing a for loop looks something like this:
<source lang="bash">
for FILE in $(ls); do [COMMAND]; done
</source>
Here is a real example that will lowercase the names of all files in the current directory:
<source lang="bash">
for FILE in $(ls); do mv $FILE $(echo $FILE | tr [A-Z] [a-z]); done
</source>
To do simple range looping, use the '''seq''' command:
<source lang="bash">
for i in `seq 1 10`; do echo "$i, "; done
</source>
== Using Find ==
The find command in Linux is very powerful, and thus somewhat complex to learn all the syntax and options.
Suffice to say that you can read the manpage and info pages to answer your questions. However, in case you are trying to figure out the prune option so that you can efficiently scan a directory for something while also ignoring .svn metadata, here is an example:
<source lang="bash">
find ./ -name .svn -prune -o -name "*html*"
</source>
Or, a more complex example: 'wcgrep', from the contrib section of the svn repo:
<source lang="bash">
#!/bin/bash
# Copyright 2004 Ben Reser <ben@reser.org>
# Licensed under the terms subversion ships under or GPLv2.
# Useful for greping in a subversion working copy.
# Essentially it behaves the same way your grep command does (in fact it
# ultimately calls the grep command on your path) with a few exceptions.
# Ignores the subversion admin directories (.svn) and vi(m) backup files.
# Recursive is always on with or without -r.
# Always print filename and line numbers.
# Ignores binary files.
# If no path is given the current working directory is searched not stdin.
# Other than that it will take any parameter or pattern your standard grep
# does.
#
# This script requires GNU findutils and by default GNU grep (though that
# can be changed with environment variables).
#
# There are three environment variables you can set that modify the default
# behavior:
#
# WCGREP_GREP Controls what command is used for the grep command.
# If unset or null wcgrep will use the command named grep.
# WCGREP_GREPARGS Controls what arguments are always passed to the grep
# command before the arguments given on the command line.
# If unset or null it defaults to -HnI (always print file
# names, line numbers and ignore binary files). If you wish
# to set no default args set the variable to a space (" ").
# WCGREP_IGNORE Controls what files are ignored by the grep command.
# This is a regex that is passed to the find command with
# -regex so see find's man page for details. If unset or
# null defaults to '.*~$\|.*/\.svn\(/\|$\)', which will
# ignore vim backup files and subversion admin dirs.
arg_count=$#
for (( i=1; i <= $arg_count; i++ )); do
arg="$1"
shift 1
if [ -z "$pattern" ]; then
if [ "$arg" == "--" ]; then
grepargs="$grepargs $arg"
pattern="$1"
shift 1
((i++))
elif [ "${arg:0:1}" != "-" ]; then
pattern="$arg"
else
grepargs="$grepargs $arg"
fi
else
pathargs="$pathargs $arg"
fi
done
find $pathargs -regex ${WCGREP_IGNORE:-'.*~$\|.*/\.svn\(/\|$\)'} -prune -o \
-type f -print0 | xargs -r0 ${WCGREP_GREP:-grep} ${WCGREP_GREPARGS:--HnI} \
$grepargs "$pattern"
</source>
== Examples ==
This script sets the svn:executable property on a number of files
<source lang="bash">
#!/bin/bash
DIRECTORIES="./example.org/htdocs/
./www.example.org/htdocs/
./security.example.org/htdocs/
./insurance.example.org/htdocs/
./hr.example.org/htdocs/"
for DIRECTORY in $DIRECTORIES
do
echo
echo "working on $DIRECTORY";
for FILE in $(find $DIRECTORY -name .svn -prune -o -type f -regex '.*s?html$'|\
grep -v .svn | xargs grep -l '\-\-\#include');
do svn propset svn:executable ON $FILE;
# do ls $FILE;
done
echo "$DIRECTORY processing complete"
echo
done
echo
echo "Finished fixing websites"
echo
</source>
==Resources==
* [http://www.gnu.org/software/bash/manual/bashref.html Bash Reference Manual]
* [http://penguinpetes.com/b2evo/index.php?title=how_the_one_liner_for_loop_in_bash_goes Penguin Pete]
* [[wp:Bash|Wikipedia page]]
[[Category:System Administration]]
[[Category:Bash]]
[[Category:Scripting]]
[[Category:Howto]]
== For Loops ==
The bash one-liner for doing a for loop looks something like this:
<source lang="bash">
for FILE in $(ls); do [COMMAND]; done
</source>
Here is a real example that will lowercase the names of all files in the current directory:
<source lang="bash">
for FILE in $(ls); do mv $FILE $(echo $FILE | tr [A-Z] [a-z]); done
</source>
To do simple range looping, use the '''seq''' command:
<source lang="bash">
for i in `seq 1 10`; do echo "$i, "; done
</source>
== Using Find ==
The find command in Linux is very powerful, and thus somewhat complex to learn all the syntax and options.
Suffice to say that you can read the manpage and info pages to answer your questions. However, in case you are trying to figure out the prune option so that you can efficiently scan a directory for something while also ignoring .svn metadata, here is an example:
<source lang="bash">
find ./ -name .svn -prune -o -name "*html*"
</source>
Or, a more complex example: 'wcgrep', from the contrib section of the svn repo:
<source lang="bash">
#!/bin/bash
# Copyright 2004 Ben Reser <ben@reser.org>
# Licensed under the terms subversion ships under or GPLv2.
# Useful for greping in a subversion working copy.
# Essentially it behaves the same way your grep command does (in fact it
# ultimately calls the grep command on your path) with a few exceptions.
# Ignores the subversion admin directories (.svn) and vi(m) backup files.
# Recursive is always on with or without -r.
# Always print filename and line numbers.
# Ignores binary files.
# If no path is given the current working directory is searched not stdin.
# Other than that it will take any parameter or pattern your standard grep
# does.
#
# This script requires GNU findutils and by default GNU grep (though that
# can be changed with environment variables).
#
# There are three environment variables you can set that modify the default
# behavior:
#
# WCGREP_GREP Controls what command is used for the grep command.
# If unset or null wcgrep will use the command named grep.
# WCGREP_GREPARGS Controls what arguments are always passed to the grep
# command before the arguments given on the command line.
# If unset or null it defaults to -HnI (always print file
# names, line numbers and ignore binary files). If you wish
# to set no default args set the variable to a space (" ").
# WCGREP_IGNORE Controls what files are ignored by the grep command.
# This is a regex that is passed to the find command with
# -regex so see find's man page for details. If unset or
# null defaults to '.*~$\|.*/\.svn\(/\|$\)', which will
# ignore vim backup files and subversion admin dirs.
arg_count=$#
for (( i=1; i <= $arg_count; i++ )); do
arg="$1"
shift 1
if [ -z "$pattern" ]; then
if [ "$arg" == "--" ]; then
grepargs="$grepargs $arg"
pattern="$1"
shift 1
((i++))
elif [ "${arg:0:1}" != "-" ]; then
pattern="$arg"
else
grepargs="$grepargs $arg"
fi
else
pathargs="$pathargs $arg"
fi
done
find $pathargs -regex ${WCGREP_IGNORE:-'.*~$\|.*/\.svn\(/\|$\)'} -prune -o \
-type f -print0 | xargs -r0 ${WCGREP_GREP:-grep} ${WCGREP_GREPARGS:--HnI} \
$grepargs "$pattern"
</source>
== Examples ==
This script sets the svn:executable property on a number of files
<source lang="bash">
#!/bin/bash
DIRECTORIES="./example.org/htdocs/
./www.example.org/htdocs/
./security.example.org/htdocs/
./insurance.example.org/htdocs/
./hr.example.org/htdocs/"
for DIRECTORY in $DIRECTORIES
do
echo
echo "working on $DIRECTORY";
for FILE in $(find $DIRECTORY -name .svn -prune -o -type f -regex '.*s?html$'|\
grep -v .svn | xargs grep -l '\-\-\#include');
do svn propset svn:executable ON $FILE;
# do ls $FILE;
done
echo "$DIRECTORY processing complete"
echo
done
echo
echo "Finished fixing websites"
echo
</source>
==Resources==
* [http://www.gnu.org/software/bash/manual/bashref.html Bash Reference Manual]
* [http://penguinpetes.com/b2evo/index.php?title=how_the_one_liner_for_loop_in_bash_goes Penguin Pete]
* [[wp:Bash|Wikipedia page]]
[[Category:System Administration]]
[[Category:Bash]]
[[Category:Scripting]]
[[Category:Howto]]
