How to assign the output of a command to a Makefile variable
Use the Make shell builtin like in MY_VAR=$(shell echo whatever) me@Zack:~$make MY_VAR IS whatever me@Zack:~$ cat Makefile MY_VAR := $(shell echo whatever) all: @echo MY_VAR IS $(MY_VAR)
shell
Is there a “standard” format for command line/shell help text?
Typically, your help output should include: Description of what the app does Usage syntax, which: Uses [options] to indicate where the options go arg_name for a required, singular arg [arg_name] for an optional, singular arg arg_name… for a required arg of which there can be many (this is rare) [arg_name…] for an arg for which … Read more
Test if remote TCP port is open from a shell script
As pointed by B. Rhodes, nc (netcat) will do the job. A more compact way to use it: nc -z <host> <port> That way nc will only check if the port is open, exiting with 0 on success, 1 on failure. For a quick interactive check (with a 5 seconds timeout): nc -z -v -w5 … Read more
Check if a file exists with a wildcard in a shell script [duplicate]
For Bash scripts, the most direct and performant approach is: if compgen -G “${PROJECT_DIR}/*.png” > /dev/null; then echo “pattern exists!” fi This will work very speedily even in directories with millions of files and does not involve a new subshell. Source The simplest should be to rely on ls return value (it returns non-zero when … Read more
Make xargs handle filenames that contain spaces
The xargs command takes white space characters (tabs, spaces, new lines) as delimiters. You can narrow it down only for the new line characters (‘\n’) with -d option like this: ls *.mp3 | xargs -d ‘\n’ mplayer It works only with GNU xargs. For MacOS: ls *.mp3 | tr \\n \\0 | xargs -0 mplayer … Read more
How do I set tmux to open specified windows at startup?
You can write a small shell script that launches tmux with the required programs. I have the following in a shell script that I call dev-tmux. A dev environment: #!/bin/sh tmux new-session -d ‘vim’ tmux split-window -v ‘ipython’ tmux split-window -h tmux new-window ‘mutt’ tmux -2 attach-session -d So everytime I want to launch my … Read more
Way to create multiline comments in Bash?
Use : ‘ to open and ‘ to close. For example: : ‘ This is a very neat comment in bash ‘
What is /dev/null 2>&1?
>> /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
Using find to locate files that match one of multiple patterns
Use -o, which means “or”: find Documents \( -name “*.py” -o -name “*.html” \) You’d need to build that command line programmatically, which isn’t that easy. Are you using bash (or Cygwin on Windows)? If you are, you should be able to do this: ls **/*.py **/*.html which might be easier to build programmatically.
Going to a specific line number using Less in Unix
With n being the line number: ng: Jump to line number n. Default is the start of the file. nG: Jump to line number n. Default is the end of the file. So to go to line number 320123, you would type 320123g. Copy-pasted straight from Wikipedia.