Revised Answer (Feb 12, 2014) the_world_is_flat=true # …do something interesting… if [ “$the_world_is_flat” = true ] ; then echo ‘Be careful not to fall off!’ fi Original Answer Caveats: https://stackoverflow.com/a/21210966/89391 the_world_is_flat=true # …do something interesting… if $the_world_is_flat ; then echo ‘Be careful not to fall off!’ fi From: Using boolean variables in Bash The reason … Read more
Use wc: wc -l <filename> This will output the number of lines in <filename>: $ wc -l /dir/file.txt 3272485 /dir/file.txt Or, to omit the <filename> from the result use wc -l < <filename>: $ wc -l < /dir/file.txt 3272485 You can also pipe data to wc as well: $ cat /dir/file.txt | wc -l 3272485 … Read more
The simplest and most widely available method to get user input at a shell prompt is the read command. The best way to illustrate its use is a simple demonstration: while true; do read -p “Do you wish to install this program? ” yn case $yn in [Yy]* ) make install; break;; [Nn]* ) exit;; … Read more
Bash Space-Separated (e.g., –option argument) cat >/tmp/demo-space-separated.sh <<‘EOF’ #!/bin/bash POSITIONAL_ARGS=() while [[ $# -gt 0 ]]; do case $1 in -e|–extension) EXTENSION=”$2″ shift # past argument shift # past value ;; -s|–searchpath) SEARCHPATH=”$2″ shift # past argument shift # past value ;; –default) DEFAULT=YES shift # past argument ;; -*|–*) echo “Unknown option $1” exit … Read more
Try mkdir -p: mkdir -p foo Note that this will also create any intermediate directories that don’t exist; for instance, mkdir -p foo/bar/baz will create directories foo, foo/bar, and foo/bar/baz if they don’t exist. Some implementation like GNU mkdir include mkdir –parents as a more readable alias, but this is not specified in POSIX/Single Unix … Read more
You can set the internal field separator (IFS) variable, and then let it parse into an array. When this happens in a command, then the assignment to IFS only takes place to that single command’s environment (to read ). It then parses the input according to the IFS variable value into an array, which we … Read more
The test command (written as [ here) has a “not” logical operator, ! (exclamation mark): if [ ! -f /tmp/foo.txt ]; then echo “File not found!” fi