Bash variables: Difference between revisions
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<metadesc>Examples of working with bash variables</metadesc> | |||
== Finding defined variables == | == Finding defined variables == | ||
Assuming you have done something like foo="bar" at your bash prompt it is not always clear how to echo ALL the defined variables back from your bash session. The following is a good way to get that information when needed. This can also be useful for debugging scripts that you are in the process of building out. | Assuming you have done something like foo="bar" at your bash prompt it is not always clear how to echo ALL the defined variables back from your bash session. The following is a good way to get that information when needed. This can also be useful for debugging scripts that you are in the process of building out. | ||
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<pre> | <pre> | ||
declare -xp | declare -xp | ||
</pre> | |||
An alternate command that will also give nice and parsable results. This is quite nice, as the loop itself will pull the values that compgen -v gave as just var names. | |||
<pre> | |||
compgen -v | while read line; do echo $line=${!line};done | |||
</pre> | |||
== Convert upper to lower case in various ways == | |||
Why bother having multiple ways to do the same thing? Merlin software on routers does not have the same tr and sed versions, and are not GNU compiled. However awk in that case does still work with its builtin tolower logic within itself. Always a good idea to know more than one way to do things. | |||
<pre> | |||
echo FooBar | awk '{print tolower($0)}' | |||
foobar | |||
</pre> | |||
<pre> | |||
echo FooBar | tr [:upper:] [:lower:] | |||
foobar | |||
</pre> | |||
<pre> | |||
echo FooBar | sed 's/[A-Z]/\L&/g' | |||
foobar | |||
</pre> | |||
== Bash builtins == | |||
From [https://www.reddit.com/r/bash/comments/12z9snv/5_inbuilt_bash_variables_that_every_developer/| reddit of all places] | |||
<pre> | |||
man bash | awk '/ Shell Variables/,/ Arrays/' | more | |||
</pre> | |||
== Bash history == | |||
Looks like it can reside in different dot files. For Ubuntu it is in ~/.bashrc | |||
<pre> | |||
HISTSIZE=2000 | |||
HISTFILESIZE=4000 | |||
</pre> | </pre> | ||
[[Category:Bash]] | [[Category:Bash]] | ||
Latest revision as of 15:02, 25 April 2024
Finding defined variables
Assuming you have done something like foo="bar" at your bash prompt it is not always clear how to echo ALL the defined variables back from your bash session. The following is a good way to get that information when needed. This can also be useful for debugging scripts that you are in the process of building out.
declare -p
If you only want the environment variables, and do not want to use env for some reason
declare -xp
An alternate command that will also give nice and parsable results. This is quite nice, as the loop itself will pull the values that compgen -v gave as just var names.
compgen -v | while read line; do echo $line=${!line};done
Convert upper to lower case in various ways
Why bother having multiple ways to do the same thing? Merlin software on routers does not have the same tr and sed versions, and are not GNU compiled. However awk in that case does still work with its builtin tolower logic within itself. Always a good idea to know more than one way to do things.
echo FooBar | awk '{print tolower($0)}'
foobar
echo FooBar | tr [:upper:] [:lower:] foobar
echo FooBar | sed 's/[A-Z]/\L&/g' foobar
Bash builtins
From reddit of all places
man bash | awk '/ Shell Variables/,/ Arrays/' | more
Bash history
Looks like it can reside in different dot files. For Ubuntu it is in ~/.bashrc
HISTSIZE=2000 HISTFILESIZE=4000