From b5cdd0f700912e6847441cacdbc05fd84771193f Mon Sep 17 00:00:00 2001 From: Scott Griffin Date: Tue, 23 Jun 2015 23:00:16 -0700 Subject: [PATCH] brace expansion example. --- README.md | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/README.md b/README.md index 0b7ef27..b484543 100644 --- a/README.md +++ b/README.md @@ -107,6 +107,10 @@ Notes: - In Bash, note there are lots of kinds of variable expansion. Checking a variable exists: `${name:?error message}`. For example, if a Bash script requires a single argument, just write `input_file=${1:?usage: $0 input_file}`. Arithmetic expansion: `i=$(( (i + 1) % 5 ))`. Sequences: `{1..10}`. Trimming of strings: `${var%suffix}` and `${var#prefix}`. For example if `var=foo.pdf`, then `echo ${var%.pdf}.txt` prints `foo.txt`. +- Shell brace expansion can help reduce having to re-type similar text. The command `echo foo{,bar,baz}` will expand to +`echo foo foobar foobaz`. This is helpful when copying/renaming files such as `cp somefile{,.bak}` which expands to +`cp somefile somefile.bak` or `mv some_{,absurdly_long_}filename` which expands to `mv some_filename some_absurdly_long_filename` + - The output of a command can be treated like a file via `<(some command)`. For example, compare local `/etc/hosts` with a remote one: ```sh diff /etc/hosts <(ssh somehost cat /etc/hosts)