When using the Linux command line and related tools, there are many useful tricks and common practices worth noting. In this post, I’m keeping a running list of tips related to Linux command-line tools for future reference.

Table of Contents

• Cd
• Command Line
• Cut
• Echo
• Expand
• Hexdump
• Git
  • Branch
• Gdb
• Grep
• Objdump
• Ps
• Readelf
• Set
• Tee

Cd

• cd - moves back to the previous directory.
• pushd <path> moves to the path and save the current directory.
  • popd to return to the saved directory.

Command Line

• ctrl-A moves cursor to the beginning of line.
• ctrl-E moves cursor to the end of the line.
• ctrl-U cuts everything from cursor to beginning of the line.
• ctrl-K cuts everything from cursor to end of the line.
• ctrl-Y yanks the last cut text.
• !! runs the previous command.

Cut

• -c11- removes the first 11 chars of each line.
• -f2 -d':' extracts the second element of each line using ‘:’ as the delimiter.

Echo

• echo $? displays the return value of the most recently run program.

Expand

• expand -t 4 <filename> outputs the file with tabs expanded as 4 spaces.

Hexdump

• hexdump -C <filename> dumps a binary file in canonical hex+ASCII format.

Git

Branch

• In case of ambiguity between file names and branch names (e.g. when both a file and a branch are named as object).
  • git checkout object -- to checkout branch.
  • git checkout -- object to checkout file.

Gdb

• See https://sourceware.org/gdb/current/onlinedocs/gdb.html/ for a super detailed doc.
• -x <filename> takes the gdb script and runs it in gdb.
• l lists 10 lines of source code around the current program counter.
  • l <n> lists 10 lines of source code around line n in the current source file.
  • l main lists 10 lines of source code around the start of function main.
  • l <filename>:<n>: lists 10 lines of source code around line n in the specified source file.
• tui can be triggered by layout <format>.
  • layout src opens a tui window with source code.
  • ctrl-X A toggles tui on/off.
  • ctrl-X O switches between tui windows.
  • layout asm opens a tui window with assembly.
  • layout regs opens a tui window with CPU registers.

Grep

• -n displays line numbers.
• -c displays just the total number of matching lines.
• -E for extended-regex pattern. For example, grep -E 'dsb|dmb|isb'.
• -v excludes matched lines.
• -m <n> shows the first n matching lines.
• --exclude=".." excludes certain filenames.
• --exclude-dir=".." excludes certain directories.
• $'' to include special charactors. For example, grep $'hello\tworld'.

Objdump

• -z shows all symbols (to include those with zero values).
• To perform objdump on arm binary,
  • For bare-metal, install binutils-arm-none-eabi, and use arm-none-eabi-objdump.
  • For arm64, install binutils-aarch64-linux-gnu, and use aarch64-linux-gnu-objdump.

Ps

• ps auxwf
  • a shows processes for all users.
  • u shows the user/owner of each process.
  • x shows processes not attached to a terminal.
  • w shows wide output (to include the entire command line).
  • f shows processes in a tree format.

Readelf

• -x dumps bytes in a section in hexadecimal format. For example readelf -x .hyp.reloc vmlinux.

Set

• When writing a shell script, use set -e at the beginning to specify that the script should exit immediately if any command exits with a non-zero status.

Tee

• <command> | tee <filename> displays the output while saving it into the file.
• <command> | tee -a <filename> displays the output while appending it at the end of the file.
• <command> 2>&1 | tee <filename> displays the stderr and stdout while saving them in the file.
  • Shorthand: <command> |& tee <filename>