Commands by fbparis (1)

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know the current running shell (the true)
Return the current shell. It is better than print $SHELL which can sometimes return a false value.

Use default value if unassigned
Will use variable value (for variable $my_dir, in this case), an assign a default value if there is none.

use jq to validate and pretty-print json output
the `jq` tool can also be used do validate json files and pretty print output `cat file.json | jq` available on several platforms, including newer debian-based systems via `#sudo apt install jq`, mac via `brew install jq`, and from source https://stedolan.github.io/jq/download/

See system users

Convert text to lowercase
Usage: lower [STRING]...

Get your outgoing IP address

Search some text from all files inside a directory

back ssh from firewalled hosts
host B (you) redirects a modem port (62220) to his local ssh. host A is a remote machine (the ones that issues the ssh cmd). once connected port 5497 is in listening mode on host B. host B just do a ssh 127.0.0.1 -p 5497 -l user and reaches the remote host'ssh. This can be used also for vnc and so on.

Extracting a range of pages from a PDF, using GhostScript
In this example we extract pages 14-17

count how many cat processes are running

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