First of all, you might want to check out the subreddit:
/r/commandline https://www.reddit.com/r/commandline/
general commands
- awk/grep/sed/wc - text file processing
- convert (image magick) - image processing tool
- cpulimit - limit the cpu usage of a process
- fdupes - check for duplicate files and optionally remove them
- pdftk - concatenate pdf files and more - https://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/
- rsync - back up tool
- tmux - terminal multiplexer - almost always my first install
- tree - view directory contents in a tree format
- zcat/zmore - display a file that is compressed (e.g. zmore /var/log/syslog.2.gz)
security/reverse engineering:
- binwalk - search binary images for embedded files
- gdb + peda - debugger with extensions - https://github.com/longld/peda
- nmap - network scanning tool
- radare2 - command line dissassembler - https://github.com/radare/radare2
- scapy - network packet crafting - https://github.com/secdev/scapy
- tshark - network traffic analyzer
- tcpdump - network traffic analyzer
- xxd - hexdump tool
Bonus:
- find - find files - I often use this to find files containing a string:
$ cat bin/findstring
#!/bin/sh
find . -type f -exec grep -i -l "$@" {} \;