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Bash

Bash manual: https://www.gnu.org/software/bash/manual/bash.html

Redirection

Print to stdout: echo "hello"
Print to stderr: echo "hello" 1>&2

Redirect stdout: 1> == >
Pipe stdout: |
Redirect stderr: 2>
Pipe stderr: 2>&1 1> /dev/null |
Redirect stderr and pipe stdout: 2> tmp.txt |
Redirect stdout and pipe stderr: 2>&1 1> tmp.txt |
Redirect stdout and stderr: &> == > tmp.txt 2>&1 == 2> tmp.txt 1>&2
Pipe stdout and stderr: 2>&1 |

Pipe stdout to a command that normally reads from a file

Startup Files

login interactive .bashrc .bash_profile* example situation example command bash options
no no no no running a script bash myscript.sh bash -c
no yes yes no launching a new shell screen bash
yes no usually** yes non-interactive login to remote computer ssh sherlock "echo hi > tmp.txt" bash -l -c
yes yes usually** yes interactive login to remote computer ssh sherlock bash -l

* Bash looks for ~/.bash_profile, ~/.bash_login, and ~/.profile, in that order, and executes commands from the first one that exists. ** By default in Ubuntu, .bashrc is sourced by .profile but exits immediately if the shell is not run interactively.

Default startup files are stored in the directory /etc/skel/ and are copied to a new user's home directory when such user is created by the useradd program.

References

Text processing

GNU Coreutils manual: https://www.gnu.org/software/coreutils/manual/coreutils.html

Extracting lines

Given

  • line numbers ($L1, $L2): sed -n "$L1,$L2p" /path/to/file
  • regex ($reg): grep -E -e $reg /path/to/file

X11 forwarding

Options

  • -C: gzip-compress all traffic - desirable on slower networks
  • -X: Enables X11 forwarding
  • -Y: Enables trusted X11 forwarding. This is less secure than -X but may be required for compatibility. On Debian (e.g., Ubuntu) systems, -X defaults to -Y.

Local software installation

Typical setup (see https://askubuntu.com/a/633924)

  • Binaries: place in $HOME/bin/ (example: $HOME/bin/pandoc)
    • Add $HOME/bin to PATH, such as in .bashrc: PATH="$HOME/bin:$PATH"
  • Man pages: place in $HOME/share/man/ (example: $HOME/share/man/man1/pandoc.1.gz)
    • Add $HOME/share/man to MANPATH, such as in .bashrc: MANPATH="$HOME/share/man:$MANPATH"