NOTE : This is a live document , will be updated in the future !
### Useful commands :
Recently, I needed a template of English alphabet to test some combinatorics ideas utilising Regex, I said I need a line of z-to-z , although be honest I could not find on Google as a first match : don't do this, better take advantage of interactive shell capabilities, I use Git bash for Windows (you may use Bash/Dash as default for your e.g. Ubuntu/Debian respectively), just type the following excluding # abcdefghijklmnopqrstuvwxyz to get the desired result as of mine recent intention i.e. to get letters of English alphabet in ascending order :
printf "%s" {a..z} # abcdefghijklmnopqrstuvwxyz
# comment_syntax
### Positional parameters :
Depending on the following scenario $0 position variable would target to :
| Interactive shell (terminal) | Non-interactive shell (file) | |
|---|---|---|
| /usr/bin/ | /source_file[.sh] |
set -- -a -b -c # initial condition
echo "$@" # -a -b -c
# to unset all positional parameters at once do the following :
shift N # N is a number starting from 1 for -a, 2 for -b, 3 for -c, etc. if let's say it's first i.e. 1 for -a the N could be omitted, otherwise must be stated e.g.:
shift 1 # same as just shift
echo "$@" # -b -c
# Where is one "BUT" shift commands removes positional parameters with behaviour of dynamic index rather than sparsed index – consider the initial condition i.e.:
set -- -a -b -c # initial condition
shift 2 # would remove -a & -b, not only -b as may be expected resulting not in -a -c, but in probably unexpected of -c only as number 2 would say remove first two of the $@
Someone might give me more eloquent example (always welcome leave a comment below) to splice positional parameters in the middle , but for now as I just started learning bash, I see this is quite bearable workaround for interactive shell specifically,e.g. :
# set -- -a -b -c # consider this was initial condition
# NOTE : consider we still on the same bash session
# just reset it with the following :
set -- -a -c
echo "$@" # -a -c
# I do understand that if those are dozen of positional parameters, that might be an issue or if you want some more dynamic usage of, otherwise for me it does a job, least for now
More is coming soon, stay tuned ! ...
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