$ cd /et<TAB>            # → /etc/
$ ls /home/<TAB><TAB>    # lists matches
$ ssh hu<TAB>            # → hunter (from SSH config)

$ ssh username@hunter-login05.hww.hlrs.de

$ scp local_file.txt username@hunter-login05.hww.hlrs.de:path/
$ scp local_file.txt username@hunter-login05.hww.hlrs.de:/absolute/path/
$ scp -r username@hunter-login05.hww.hlrs.de:results ./

$ rsync -av local_dir/ username@hunter-login05.hww.hlrs.de:remote_dir/

Host hunter
    HostName       hunter-login05.hww.hlrs.de
    User           <your_HLRS_login>
    IdentityFile   ~/.ssh/HLRS_cs_YYYYMMDD
    IdentitiesOnly yes
    PreferredAuthentications   publickey,keyboard-interactive
    ServerAliveInterval 60
    ServerAliveCountMax 5

$ ssh hunter
$ scp local_file.txt hunter:
$ rsync -av local_dir/ hunter:remote_dir/

Host hunter
    HostName       hunter-login05.hww.hlrs.de
    User           <your_HLRS_login>
    IdentityFile   C:\Users\<username>\.ssh\HLRS_cs_YYYYMMDD
    IdentitiesOnly yes
    PreferredAuthentications   publickey,keyboard-interactive
    ServerAliveInterval 60
    ServerAliveCountMax 5

$ mkdir -p ~/.ssh && chmod 700 ~/.ssh
$ cp /drives/c/Users/lucas/.ssh/HLRS_cs_20250728 ~/.ssh/
$ chmod 600 ~/.ssh/HLRS_cs_20250728

$ pwd
/home/user/documents

$ cd /absolute/path
$ cd ..   # up one level
$ cd ~    # home
$ cd -    # previous

$ ls
$ ls -l   # detailed
$ ls -la  # + hidden
$ ls -lh  # human readable

$ cat file.txt

$ less large_file.log    # Navigate with arrow keys,
                         # q to quit, /pattern to search

$ head -n 20 file.txt    # First 20 lines
$ tail -n 10 output.log  # Last 10 lines
$ tail -f output.log     # Follow file in real time

$ touch newfile.txt

$ mkdir new_directory
$ mkdir -p parent/child/grandchild   # Create nested dirs

$ cp source.txt destination.txt
$ cp -r source_dir/ dest_dir/   # Copy directory recursively

$ mv file.txt new_location/
$ mv old_name.txt new_name.txt

$ rm file.txt
$ rm -r directory/   # Remove directory and contents

$ find . -name "*.csv"                  # Find by name pattern
$ find /home -type d -name "results"    # Find directories only
$ find . -name "*.log" 2>/dev/null      # Suppress permission errors

$ which python
/usr/bin/python

$ man grep        # Open the manual for grep
$ man -k search   # Search for commands by keyword
$ ls --help       # Quick built-in help (most commands support it)

$ chmod u+x script.sh         # add execute for owner
$ chmod go-w file.txt         # remove write for group & others
$ chmod -R g+rX shared_data/  # +r on all, +x on directories only (capital X)
$ chmod -R g+rx shared_data/  # AVOID on data: marks every file executable

$ chmod 755 script.sh    # rwxr-xr-x
$ chmod 600 secret.key   # rw-------
$ chmod 750 shared_data/          # group can enter/ls
$ chmod 640 shared_data/file.txt  # group can read

$ id                            # your groups
$ chgrp -R mygroup shared_data/ # assign group
$ chmod g+s shared_data/        # new files inherit the group
$ chmod -R g+rX shared_data/    # group read + traverse
$ namei -l $PWD/shared_data/    # check the whole path

$ ws_share share my_workspace alice   # grant read access
$ ws_share share my_workspace bob
$ ws_share list my_workspace          # who has access
$ ws_share unshare my_workspace bob   # revoke one
$ ws_share unshare-all my_workspace   # revoke all

$ echo $PATH                          # View a variable
$ export MY_VAR="hello"               # Set a variable
$ export PATH=$PATH:/my/custom/bin    # Extend PATH

$ touch "my file.txt"        # filename with a space
$ echo "$HOME"               # expands variable
$ echo '$HOME'               # prints literal $HOME
$ grep "TODO list" notes.txt # multi-word pattern

$ FILE=""
$ rm $FILE        # → "rm" with no args (unhelpful error)
$ rm "$FILE"      # → rm: cannot remove '': clearer error

$ ls my file.txt          # lists "my" and "file.txt" separately
$ ls "my file.txt"        # correct
$ ls my\ file.txt         # also correct: escape the space
$ cp my file.txt /tmp/    # copies "my" and "file.txt" separately
$ cp "my file.txt" /tmp/  # correct

$ ls /etc /nonexistent > out.txt       # only stdout → file
$ ls /etc /nonexistent 2> err.txt      # only stderr → file
$ ls /etc /nonexistent > all.txt 2>&1  # both → same file
$ command < input.txt                  # stdin from file

$ find / -name "*.conf" 2>/dev/null # discard "Permission denied"

$ ls -l | grep ".txt"                    # filter for .txt files
$ cat job.out | grep "ERROR" | wc -l     # count errors in job output
$ ls -lh *.log | sort -k5 -h | tail -n 5 # largest 5 log files

$ diff <(sort file1.txt) <(sort file2.txt) # compare sorted versions

$ ./simulation | tee output.log     # see output AND save to file
$ ./simulation | tee -a output.log  # append instead of overwrite

$ grep "error" logfile.txt      # lines containing "error"
$ grep -i "warning" logfile.txt # case-insensitive
$ grep -v "debug" logfile.txt   # lines NOT matching
$ grep -r "TODO" src/           # search recursively
$ grep -c "error" logfile.txt   # count matching lines

$ grep -A 3 "FATAL" logfile.txt    # 3 lines After match
$ grep -B 2 "FATAL" logfile.txt    # 2 lines Before match
$ grep -C 2 "FATAL" logfile.txt    # 2 lines of Context

$ grep -v "^#" config.cfg            # skip comment lines
$ grep "node[0-9][0-9]" hosts.txt    # character class
$ grep -E "warn|error|fatal" app.log # alternation

$ ps aux                    # List all running processes
$ ps aux | grep python      # Filter for a specific program

$ kill 1234                 # Terminate process by PID
$ kill -9 1234              # Force kill
$ long_process &            # Run in background
$ jobs                      # List background jobs
$ fg %1                     # Bring job 1 to foreground

$ tar -czf archive.tar.gz my_dir/     # Create compressed archive
$ tar -xzf archive.tar.gz             # Extract archive
$ tar -tzf archive.tar.gz             # List contents without extracting

$ du -sh */                        # size of each subdirectory
$ du -sh * | sort -hr | head -10   # top 10 largest items
$ df -h                            # filesystem disk space usage
$ find . -name "*.log" -size +100M # logs over 100MB

$ wc -l results/*.csv       # count lines in all CSV files
$ sort -nr sizes.txt | head # top 10 largest values

$ watch -n 5 'ls -lh output/'  # monitor output directory every 5s

$ find . -name "*.csv" \
  | xargs wc -l \
  | sort -nr \
  | head -5