Life on the command line on Linux is clearly one thing most of us take pleasure in, however typing the identical command repeatedly can develop into tiresome. To keep away from that boredom, this put up explains plenty of methods that you may make repeating instructions – or repeating instructions however with some modifications – lots simpler than you may count on.
Rerunning the earlier command
First, the best approach to repeat a command is just by typing !!. If you happen to have been logged right into a Linux server and ready for a coworker to log in, for instance, you may wish to repeat the who command proven beneath till you see your coworker’s username. Typing !! after the preliminary who command will do that for you.
$ who | awk '{print $1,$2}'
shs pts/1
$ !!
shs pts/1
$ !!
shs pts/1
nemo pts/2 <== Yay, he simply confirmed up!
Exploring your command historical past
Historical past recordsdata are usually pretty lengthy – usually holding 1,000 instructions or extra. You may view what number of instructions shall be remembered on your account by utilizing this command:
$ echo $HISTSIZE 1000
Nevertheless, you do not have to take a look at lots of or 1000’s of prior instructions if you wish to view your command historical past. You may have a look at solely the newest instructions by specifying what number of prior instructions you wish to have displayed. This command will solely present the newest 5 instructions:
$ historical past 5
1011 28/07/22 14:14:04 who | awk '{print $1,$2}'
1012 28/07/22 14:15:18 vi timetable
1013 28/07/22 14:15:43 who | awk '{print $1,$2}'
1014 28/07/22 14:21:57 echo $HISTSIZE
1015 28/07/22 14:24:39 historical past 5
Reusing instructions out of your command historical past
One other simple approach to repeat instructions is to reference your command historical past by typing one thing just like the instructions beneath that might rerun the command in your historical past command output after you discover it utilizing grep, after which sort ! adopted by the sequence quantity related to the command.
$ historical past | grep Sydney 865 27/07/22 12:02:50 date -d 'TZ="Australia/Sydney" 04:30 subsequent Monday' $ !865 date -d 'TZ="Australia/Sydney" 04:30 subsequent Monday' Solar Jul 31 02:30:00 PM EDT 2022
Rerunning instructions with modifications
It’s also possible to rerun instructions however change them within the course of. For instance, should you typed “echo whats up there”, you can use !! adopted by a : and the string that replaces “there” with “world” to run it once more:
$ echo whats up, there whats up, there $ !!:s/there/world/ echo whats up, world
Within the case of echoing “whats up”, it might be simpler to simply sort “echo whats up, world”, however for a lot of instructions, this may not be the case. If you happen to wished to take a look at a calendar for the month of August over a interval of some variety of years, for instance, you can run instructions like these (output not proven):
$ cal aug 2020 $ !!:s/020/021/ $ !!:s/1/2/
Do not forget that !! recollects the command that was run, not what you typed to create it. So, the second command replaces “2020” with “2021” and the third replaces “2021” with “2022”.
It’s also possible to reuse instructions out of your command historical past on this manner. This is an instance that reruns a command in your command historical past changing “at the moment” with “tomorrow”:
$ !1012:s/at the moment/tomorrow/
Avoiding saving instructions to your command historical past
It’s also possible to resolve not to avoid wasting the instructions that you’ve got utilized in your present login session in your historical past file by operating a command like this one:
$ unset HISTFILE && exit
That command will exit the session with out saving any of the instructions.
It’s also possible to use the HISTIGNORE setting to keep away from saving instructions that shall be a lot simpler to sort once more than discover in your command historical past. For instance, you may not wish to trouble storing instructions like cd, ls, pwd, clear, man or historical past in your .historical past file because you would not prone to seek advice from your command historical past to reuse them.
$ grep HISTIGNORE .bashrc HISTIGNORE="cd:pwd:clear:ls:man:historical past"
Reusing a command argument
One other attention-grabbing trick is to reuse a command argument as in following instructions. The $_ within the second command represents the final argument within the first command. The instructions beneath create a brand new listing after which transfer into it with out having to sort the listing path a second time.
$ mkdir /residence/$USER/instruments/mytools/settings $ cd $_
The instance command beneath confirms that $_ solely captures the ultimate piece of textual content:
$ echo Have a pleasant day! $ echo $_ day!
Reusing a portion of a command
If you wish to create a collection of directories with names starting with the present date however adopted by a set of extra endings, you can use a command like this to make it rather less bother:
$ mkdir -v `date '+%Ypercentmpercentd'`_{reviews,pictures,notes}
mkdir: created listing '20220728_reports'
mkdir: created listing '20220728_images'
mkdir: created listing '20220728_notes'
The -v possibility used with the mkdir command gives the affirmation that every listing was created.
If you might want to create a listing construction like what’s proven above routinely, it might in all probability be a good suggestion to show a command like that into an alias in order that it’s simple to reuse.
Saving your instructions as aliases
After all, one of many best methods to repeat instructions that you just use usually, particularly advanced ones, is to easily flip them into aliases and save these aliases in your .bashrc file in order that they’re accessible each time you log in.
The alias beneath creates a listing of all the months of the 12 months of their correct order.
$ alias show_months="printf "%02d/01/2000n" {1..12} | LC_ALL=C date +%B -f-"
$ show_months
January
February
March
April
Could
June
July
August
September
October
November
December
Bear in mind to provide your aliases significant names so to use them with out having to seek for them in your .bashrc file each time.
Wrap-up
There are loads of methods to make Linux instructions, particularly advanced instructions, simpler to repeat. Let’s preserve making engaged on the command line enjoyable.
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