Differences

This shows you the differences between two versions of the page.

--- linux:shell [2024/04/19 09:30]
cyril better solution for recursive exec
+++ linux:shell [2024/04/21 14:03]
cyril [Misc]
@@ Line 1: / Line 1: @@
 ====== Shell ======
+===== Block comment =====
+With "END" being just an example of any random string that must not appear in the commented section:
+<code bash>
+: << 'END'
+sleep 1
+END
+</code>
+===== Iterate over a list as a string =====
+Different options:
+<code bash>
+# option 1, without variable
+for x in a b c; do echo $x; done
+# option 2, with string
+list="a b c"
+for x in $list; do echo $x; done         # only works with sh and bash
+for x in ${=list}; do echo $x; done      # only works with zsh
+for x in $(echo $list}; do echo $x; done # works with any shell
+# option 3, with an array
+list=(a b c)
+for x in $list; do echo $x; done
+</code>
 ===== Do something recursively on all files =====
-Use bash, with ''{}'' being the file name:
+Use ''find'', with ''{}'' being the file name:
 <code bash>
 find . -type f -exec <command> {} \;
@@ Line 35: / Line 62: @@
 search_dir "."
+</code>
+===== Misc =====
+  * **Default value for variable**: <code bash>
+${<variable>:-<default-value>}
+</code>
+  * **Get directory of current script** (for instance in order to run a script that is stored in the same directory, or in a known relative path):<code bash>
+BASEDIR=$(dirname "$0")
+</code>
+  * **echo to stderr**, just redirect the output:<code bash>
+echo "foo" 1>&2
+</code>
+  * **Convert dash-time to ISO** (2024-04-21_15-50-30 to 2024-04-21T15:50:30, for instance to use it as input for ''date''): <code bash>
+sed -r "s/([0-9]{4})-([0-9]{2})-([0-9]{2})_([0-9]{2})-([0-9]{2})-([0-9]{2})/\1-\2\-3T\4:\5:\6/"
+</code>
+  * **Get target name of symbolic link**:<code bash>
+readlink <symbolic-link>
+</code>
+  * **Execute command**:<code bash>
+var=`cat file`
+var=$(cat file)
+</code>
+  * **Evaluate mathematical expression** (''zsh'' also supports floating-point operations):<code bash>
+echo $((2*3))
+</code>
+  * **time with redirected output** (also works for groups of commands):<code bash>
+time (cat file1 > file2)
+time (cat file1 > /dev/null; sync)
+</code>
+  * **Check number of arguments and print usage:**<code bash>
+if [[ $# -lt 2 ]]; then
+        echo "Usage: foo.sh <arg1> <arg2>" 1>&2
+        exit 1
+fi
 </code>