Echo command, and then run it? (Like make)

Question

Is there some way to get bash into a sort of verbose mode where, such that, when it\'s running a shell script, it echoes out the command it\'s going to run before running it? T

Answer 1

To add to others' implementations, this is my basic script boilerplate, including argument parsing (which is important if you're toggling verbosity levels).

#!/bin/sh

# Control verbosity
VERBOSE=0

# For use in usage() and in log messages
SCRIPT_NAME="$(basename $0)"

ARGS=()

# Usage function: tells the user what's up, then exits.  ALWAYS implement this.
# Optionally, prints an error message
# usage [{errorLevel} {message...}
function usage() {
    local RET=0
    if [ $# -gt 0 ]; then
        RET=$1; shift;
    fi
    if [ $# -gt 0 ]; then
        log "[$SCRIPT_NAME] ${@}"
    fi
    log "Describe this script"
    log "Usage: $SCRIPT_NAME [-v|-q]" # List further options here
    log "   -v|--verbose    Be more verbose"
    log "   -q|--quiet      Be less verbose"
    exit $RET
}

# Write a message to stderr
# log {message...}
function log() {
    echo "${@}" >&2
}

# Write an informative message with decoration
# info {message...}
function info() {
    if [ $VERBOSE -gt 0 ]; then
        log "[$SCRIPT_NAME] ${@}"
    fi
}

# Write an warning message with decoration
# warn {message...}
function warn() {
    if [ $VERBOSE -gt 0 ]; then
        log "[$SCRIPT_NAME] Warning: ${@}"
    fi
}

# Write an error and exit
# error {errorLevel} {message...}
function error() {
    local LEVEL=$1; shift
    if [ $VERBOSE -gt -1 ]; then
        log "[$SCRIPT_NAME] Error: ${@}"
    fi
    exit $LEVEL
}

# Write out a command and run it
# vexec {minVerbosity} {prefixMessage} {command...}
function vexec() {
    local LEVEL=$1; shift
    local MSG="$1"; shift
    if [ $VERBOSE -ge $LEVEL ]; then
        echo -n "$MSG: "
        local CMD=( )
        for i in "${@}"; do
            # Replace argument's spaces with ''; if different, quote the string
            if [ "$i" != "${i/ /}" ]; then
                CMD=( ${CMD[@]} "'${i}'" )
            else
                CMD=( ${CMD[@]} $i )
            fi
        done
        echo "${CMD[@]}"
    fi
    ${@}
}

# Loop over arguments; we'll be shifting the list as we go,
# so we keep going until $1 is empty
while [ -n "$1" ]; do
    # Capture and shift the argument.
    ARG="$1"
    shift
    case "$ARG" in
        # User requested help; sometimes they do this at the end of a command
        # while they're building it.  By capturing and exiting, we avoid doing
        # work before it's intended.
        -h|-\?|-help|--help)
            usage 0
            ;;
        # Make the script more verbose
        -v|--verbose)
            VERBOSE=$((VERBOSE + 1))
            ;;
        # Make the script quieter
        -q|--quiet)
            VERBOSE=$((VERBOSE - 1))
            ;;
        # All arguments that follow are non-flags
        # This should be in all of your scripts, to more easily support filenames
        # that start with hyphens.  Break will bail from the `for` loop above.
        --)
            break
            ;;
        # Something that looks like a flag, but is not; report an error and die
        -?*)
            usage 1 "Unknown option: '$ARG'" >&2
            ;;
        #
        # All other arguments are added to the ARGS array.
        *)
            ARGS=(${ARGS[@]} "$ARG")
            ;;
    esac
done
# If the above script found a '--' argument, there will still be items in $*;
# move them into ARGS
while [ -n "$1" ]; do
    ARGS=(${ARGS[@]} "$1")
    shift
done

# Main script goes here.

Later...

vexec 1 "Building myapp.c" \
    gcc -c myapp.c -o build/myapp.o ${CFLAGS}

Note: This will not cover piped commands; you need to bash -c those sorts of things, or break them up into intermediate variables or files.