>> /dev/null redirects standard output (stdout) to /dev/null, which discards it. (The >> seems sort of superfluous, since >> means append while > means truncate and write, and either appending to or writing to /dev/null has the same net effect. I usually just use > for that reason.) 2>&1 redirects standard error (2) to standard … Read more
From here: $@ behaves like $* except that when quoted the arguments are broken up properly if there are spaces in them. Take this script for example (taken from the linked answer): for var in “$@” do echo “$var” done Gives this: $ sh test.sh 1 2 ‘3 4’ 1 2 3 4 Now change … Read more
$$ is the process ID (PID) in bash. Using $$ is a bad idea, because it will usually create a race condition, and allow your shell-script to be subverted by an attacker. See, for example, all these people who created insecure temporary files and had to issue security advisories. Instead, use mktemp. The Linux man … Read more
The bug #712 suggests that make does not handle names with spaces. Nowhere, never. I found a blog post saying it’s partially implemented by escaping the spaces with \ (\\ seems to be typo or formatting artefact), but: It does not work in any functions except $(wildcard). It does not work when expanding lists of … Read more
This is the exit status of the last executed command. For example the command true always returns a status of 0 and false always returns a status of 1: true echo $? # echoes 0 false echo $? # echoes 1 From the manual: (acessible by calling man bash in your shell) ? Expands to … Read more
This is Bash-only: echo “${@: -1}”
bash –rcfile <(echo ‘. ~/.bashrc; some_command’) dispenses the creation of temporary files. Question on other sites: https://serverfault.com/questions/368054/run-an-interactive-bash-subshell-with-initial-commands-without-returning-to-the https://unix.stackexchange.com/questions/123103/how-to-keep-bash-running-after-command-execution
As pointed by B. Rhodes, nc (netcat) will do the job. A more compact way to use it: nc -z <host> <port> That way nc will only check if the port is open, exiting with 0 on success, 1 on failure. For a quick interactive check (with a 5 seconds timeout): nc -z -v -w5 … Read more
Unix shells operate a series of transformations on each line of input before executing them. For most shells it looks something like this (taken from the Bash man page): initial word splitting brace expansion tilde expansion parameter, variable and arithmetic expansion command substitution secondary word splitting path expansion (aka globbing) quote removal Using $cmd directly … Read more
\b in regular expressions match word boundaries (i.e. the location between the first word character and non-word character): $ echo “bar embarassment” | sed “s/\bbar\b/no bar/g” no bar embarassment