Differences

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

--- linux:shell [2024/04/21 13:43]
cyril
+++ linux:shell [2024/12/11 09:40] (current)
cyril [Misc]
@@ Line 72: / Line 72: @@
 BASEDIR=$(dirname "$0")
 </code>
-  * **echo to stderr**, just redirect the output:<code>
+  * **echo to stderr**, just redirect the output:<code bash>
 echo "foo" 1>&2
 </code>
+  * **Convert dash-time to ISO** (2024-04-21_15-50-30 to 2024-04-21T15:50:30, for instance to use it as input for ''date''): <code bash>
+sed -r "s/([0-9]{4})-([0-9]{2})-([0-9]{2})_([0-9]{2})-([0-9]{2})-([0-9]{2})/\1-\2\-3T\4:\5:\6/"
+</code>
+  * **Get target name of symbolic link**:<code bash>
+readlink <symbolic-link>
+</code>
+  * **Execute command**:<code bash>
+var=`cat file`
+var=$(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 [[ $# -lt 2 ]]; then
+        echo "Usage: foo.sh <arg1> <arg2>" 1>&2
+        exit 1
+fi
+</code>
+  * **Load command output as a file:**<code>
+diff <(grep x file1) <(grep y file2)
+</code>
+  * **Remove extension from file name:**<code>
+${f%.png} # with all shells
+${f:r}    # only zsh
+</code>