From documentation of set -e: When this option is on, if a simple command fails for any of the reasons listed in Consequences of Shell Errors or returns an exit status value > 0, and is not part of the compound list following a while, until, or if keyword, and is not a part of … Read more
Usage of the $ like ${HOME} gives the value of HOME. Usage of the $ like $(echo foo) means run whatever is inside the parentheses in a subshell and return that as the value. In my example, you would get foo since echo will write foo to standard out
It’s called a shebang, and tells the parent shell which interpreter should be used to execute the script. #!/bin/sh <——— bourne shell compatible script #!/usr/bin/perl <– perl script #!/usr/bin/php <— php script #!/bin/false <—— do-nothing script, because false returns immediately anyways. Most scripting languages tend to interpret a line starting with # as comment and … Read more
Yeah, yeah, the question is over a year old, but maybe I can add something useful: How to cron something at a random offset 20 times a day between 9am and 11pm? That’s kinda tricky within cron, because you are dividing 14 hours by 20 execution times. I don’t like the other answers very much … Read more
This should work: #!/bin/bash if [ “$#” -eq 0 ] || [ “$#” -gt 1 ] ; then echo “hello” fi I’m not sure if this is different in other shells but if you wish to use <, >, you need to put them inside double parenthesis like so: if ((“$#” > 1)) …
[*] Always use “$x”, at least at first. The cases where this is correct far outnumber the cases where it may be wrong. Parameter expansions are subject to both word-splitting and pathname expansion, neither of which you usually want. Quoting the expansion preserves the literal content of the parameter. Compare $ x=”foo * bar” $ … Read more
/bin/sh is usually some other shell trying to mimic The Shell. Many distributions use /bin/bash for sh, it supports source. On Ubuntu, though, /bin/dash is used which does not support source. Most shells use . instead of source. If you cannot edit the script, try to change the shell which runs it.
grep -v -x -f f2 f1 should do the trick. Explanation: -v to select non-matching lines -x to match whole lines only -f f2 to get patterns from f2 One can instead use grep -F or fgrep to match fixed strings from f2 rather than patterns (in case you want remove the lines in a … Read more
The POSIX-shell (sh) counterpart of $BASH_SOURCE is $0. see bottom for background info Caveat: The crucial difference is that if your script is being sourced (loaded into the current shell with .), the snippets below will not work properly. explanation further below Note that I’ve changed DIR to dir in the snippets below, because it’s … Read more
bash looks at the value of $argv[0] (bash is implemented in C) to determine how it was invoked. Its behavior when invoked as sh is documented in the manual: If Bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible, while conforming … Read more