command-codes

=Quick Reference= This is a quick reference guide to the meaning of some of the less easily guessed commands and codes. ( ... ) || Function definition || function myfunc { echo hello } ||
 * ~ Command ||~ Description ||~ Example ||
 * ~ & || Run the previous command in the background || ls & ||
 * ~ && || Logical AND || if [ "$foo" -ge "0" ] && [ "$foo" -le "9"] ||
 * ~ ¦¦ || Logical OR || if [ "$foo" -lt "0" ] ¦¦ [ "$foo" -gt "9" ] (not in Bourne shell)||
 * ~ ^ || Start of line || grep "^foo" ||
 * ~ $ || End of line || grep "foo$" ||
 * ~ **=** || String equality (cf. -eq) || if [ "$foo" "bar" ] ||
 * ~ ! || Logical NOT || if [ "$foo" != "bar" ] ||
 * ~ $$ || PID of current shell || echo "my PID = $$" ||
 * ~ $! || PID of last background command || ls & echo "PID of ls = $!" ||
 * ~ $? || exit status of last command || ls ; echo "ls returned code $?" ||
 * ~ $0 || Name of current command (as called) || echo "I am $0" ||
 * ~ $1 || Name of current command's first parameter || echo "My first argument is $1" ||
 * ~ $9 || Name of current command's ninth parameter || echo "My ninth argument is $9" ||
 * ~ $@ || All of current command's parameters (preserving whitespace and quoting) || echo "My arguments are $@" ||
 * ~ $* || All of current command's parameters (not preserving whitespace and quoting) || echo "My arguments are $*" ||
 * ~ -eq || Numeric Equality || if [ "$foo" -eq "9" ] ||
 * ~ -ne || Numeric Inquality || if [ "$foo" -ne "9" ] ||
 * ~ -lt || Less Than || if [ "$foo" -lt "9" ] ||
 * ~ -le || Less Than or Equal || if [ "$foo" -le "9" ] ||
 * ~ -gt || Greater Than || if [ "$foo" -gt "9" ] ||
 * ~ -ge || Greater Than or Equal || if [ "$foo" -ge "9" ] ||
 * ~ -z || String is zero length || if [ -z "$foo" ] ||
 * ~ -n || String is not zero length || if [ -n "$foo" ] ||
 * ~ -nt || Newer Than || if [ "$file1" -nt "$file2" ] ||
 * ~ -d || Is a Directory || if [ -d /bin ] ||
 * ~ -f || Is a File || if [ -f /bin/ls ] ||
 * ~ -r || Is a readable file || if [ -r /bin/ls ] ||
 * ~ -w || Is a writable file || if [ -w /bin/ls ] ||
 * ~ -x || Is an executable file || if [ -x /bin/ls ] ||
 * ~ parenthesis: