diff --git a/README.md b/README.md index dda9dfa..84ff7d0 100644 --- a/README.md +++ b/README.md @@ -138,7 +138,7 @@ Notes: # continue in original dir ``` -- 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: $0 input_file}`. Using a default value if a variable is empty: `${name:-default}`. If you want to have an additional (optional) parameter added to the previous example, you can use something like `output_file=${2:-logfile}`. If $2 is omitted and thus empty, `output_file` will be set to `logfile`. Arithmetic expansion: `i=$(( (i + 1) % 5 ))`. Sequences: `{1..10}`. Trimming of strings: `${var%suffix}` and `${var#prefix}`. For example if `var=foo.pdf`, then `echo ${var%.pdf}.txt` prints `foo.txt`. +- In Bash, note there are lots of kinds of variable expansion. Checking a variable exists: `${name:?error message}`. For example, if a Bash script requires a single argument, just write `input_file=${1:?usage: $0 input_file}`. Using a default value if a variable is empty: `${name:-default}`. If you want to have an additional (optional) parameter added to the previous example, you can use something like `output_file=${2:-logfile}`. If `$2` is omitted and thus empty, `output_file` will be set to `logfile`. Arithmetic expansion: `i=$(( (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`. - Brace expansion using `{`...`}` can reduce having to re-type similar text and automate combinations of items. This is helpful in examples like `mv foo.{txt,pdf} some-dir` (which moves both files), `cp somefile{,.bak}` (which expands to `cp somefile somefile.bak`) or `mkdir -p test-{a,b,c}/subtest-{1,2,3}` (which expands all possible combinations and creates a directory tree).