Unix Shell

Updated: 06 August 2024

Searching

You can use grep to search in a file

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grep "hello" ./hello.txt

Or recursively through a directory:

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grep -R "hello" ./hello

And using a RegEx

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grep -R ^hello

Or case inensitive with -i or for full words with -w

You can even search for something in the output of a command using a pipe (|)

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echo "hello world" | grep "world"

Processes

List Processes

To kill a process you can first list running processes

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lsof

To get the PID of a process you can use lsof along with grep, e.g. find a node process:

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lsof | grep node

Find A Process on a Current Port

E.g for a processs running on port 4001

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lsof -i:4001

You can also just get the port by adding -t:

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lsof -t -t:4001

Kill a Process by PID

You can kill a process using it’s PID using:

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kill 1234

Or with -9 to force

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kill -9 1234

Kill a Process by Port

You can kill a process that’s listening on a port by first getting the PID of the process with lsof -t -i:<PORT NUMBER> and pass it into the kill command, e.g. for port 4000

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kill $(lsof -t -i:4000)

Jobs/Background Processes

Start a process, e.g. ping

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ping google.com

The use ctrl+z to suspend the task into the background

You can now use the terminal and start other jobs

Once jobs are running you can use jobs to view runnning jobs:

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jobs
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# which outputs
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[1]    suspended  ping google.com
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[2]  - suspended  ping other.com
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[3]  + suspended  ping hello.com

Jobs can be resumed using fg for the most recent job, or fg %<JOB NUMBER> to resume a specific job

For example, resuming the ping hello.com can be done with:

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fg %3

Navigating

You can use cd to move to specific folders relatively

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cd ../other-folder/my-folder

Or even from the user home directory by prefixing with ~

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cd ~/my-stuff

And you can use - to just swap back to the last directory

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# before, in apps/stuff, now in apps/something-else
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cd -
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# after, now in apps/something-else

Tail/Watch a file as it changes

You can get the tail of a file and watch it as it changes using:

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tail -f ./path/to/file