Shell Programs

• Two types of syntax: sh/ksh/ash/bash/dash, and csh/tcsh

Arithmetic

• expr 4 + 1 (prints 5)
• seq 1 4 (prints 1 2 3 4)

Command-line Substitutions

• Wildcard file names (e.g. cat *.c → cat file1.c file2.c)
• Backquote: Run a command and embed its output (e.g. i=expr $i + 1)

Variables

• Assigning Variables: var=value
• Using Variables: echo “$var” (remember to double quote!)
• PATH: A varaible that specify where to search for binary packages
• Variable Between Strings: “abc${x}abc” puts $x between strings

IO

• read: Space-separated inputs, put the rest in the last variable. (e.g. read a b c)
• Redirect input/output to file: program <stdin >stdout 2>stderr
  • Redirect stdout to stderr: program >&2 Redirect stderr to stdout: program 2>&1
  • Append to file: program >> stdout_file
  • Here Text: program <<EOF …stdin content… EOF (If <<\EOF is used with backslash, backslash inside content won’t be parsed)

Command-Line Arguments

• $#: Number of arguments passed in
• ${n}: The n-th argument (e.g. $1 is the 1st argument)
• $*: All arguments as a string (all quotation will be collapsed into one string)