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This article is a cheat sheet for things you learn to do in Bash (The Bourne Again Shell). Also, see the page of [[one-liners]]
== For Loops ==
<source lang="bash">
for i in `seq 1 10`; do echo "$i, "; done
</source>
== Arrays ==
In Bash v4 you can use multi-dimensional array but if you might want to use a different language. See http://wiki.bash-hackers.org/syntax/arrays for more.
Simple arrays work like the following:
<source lang="bash">
#!/bin/bash
# declare three arrays
# you can use the 'declare' built-in, but don't have to
# declare -a breakfast=('eggs' 'pancakes' 'cereal')
breakfast=('eggs' 'pancakes' 'cereal')
lunch=('sandwich' 'salad' 'smoothie')
dinner=('pasta' 'stir-fry' 'burritos')
# Now how do we loop through them?
# We could just output the values for breakfast
for i in "${breakfast[@]}"
# for BASH 3+ we have ! to access the numeric index
for i in "${!breakfast[@]}"
# Or, Build a sequence to loop through the other arrays by index
# while using a counter that is more friendly
# Arrays are indexed using integers and are zero-based
# the index number (starting at zero) gives that element
for (( i=1; i<${#breakfast}; i++ ))
do
echo "Here is the menu for day ${i}"
echo "breakfast: ${breakfast[$i-1]}"
echo "lunch: ${lunch[$i-1]}"
echo "dinner: ${dinner[$i-1]}"
done
declare -a fruits=('apples' 'oranges' 'banannas')
declare -a vegetables=('broccoli' 'onions' 'peppers' 'potatoes' 'carrots')
# the # character gives us the count of the array
echo "we have ${#fruits[@]} fruits available"
printf "%s\n" "${fruits[@]}"
echo "we have ${#vegetables[@]} vegetables available"
printf "%s\n" "${vegetables[@]}"
</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. === Mime report ===This example finds and counts files by their extension. However, A "poor-man's mime-report"<source lang="bash" line>for x in \ $(find . -maxdepth 1 -type d | \ sort | \ grep -v ^./$ ); \do \ echo -e "\n\n$x\n"; \ find "$x" -type f | \ egrep -o '\.(.?.?..)$' | \ sort | \ uniq -c ; \done</source>Breakdown:<pre> 1. stuff everything up to the semicolon into a loop variable named '$x' 2. look for directories that are immediate descendants of the current directory 3. sort them 4. don't include the current directory 6. with these: echo the name of the directory as a 'heading' in the report 7. find the files per directory 8. match only on the extensions found (between two and four-letter extensions) 9. sort them10. count and summarize by unique values</pre> But it looks more impressive as a one-liner:<source lang="bash">for x in $(find . -maxdepth 1 -type d|sort|grep -v ^./$); do echo -e "\n\n$x\n"; find "$x" -type f | egrep -o '\.(.?.?..)$' | sort | uniq -c ; done</source> === Prune ===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*"
/proc
/media/disk/backups
</source>
=== Move a directory up one level ===
Sometimes you can end up with a directory which is nested inside it's intended destination. For example, <code>drush archive-restore (arr)</code> can leave you with <tt>/var/www/drush/drush</tt> and you want the contents of the sub-directory to be at the location of it's parent. Using the BASH shell options for glob control, you can set dotglob and later unset it to be able to move * up. This worked for me on one host, and didn't work on another. For the one that didn't work, mv kept complaining that destination directories were not empty. I don't care if the destination directories exist.... that's the whole point. Uggh!
<source lang="bash">
cd /var/www/drupal/drupal/
shopt -s dotglob
mv -- * ..
shopt -u dotglob
</source>
==Resources==
* greycat ([http://wooledge.org/~greg/ Greg Wooledge]) Wiki http://mywiki.wooledge.org/EnglishFrontPage maintained by lhunath (Maarten Billemont)
* http://bash.cyberciti.biz/guide/Main_Page an excellent BASH and Linux wiki site
* http://wiki.bash-hackers.org/scripting/style
* [http://mywiki.wooledge.org/BashGuide Maarten Billemont's Bash Guide]
* [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]]
* [https://ss64.com/bash/test.html Bash tests] <code>-f -d -x -w -Z </code> What do all the file test options mean?
[[Category:System Administration]]