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Files

Parsing a key=val file.

This could be used to parse a simple key=value configuration file.

# Setting 'IFS' tells 'read' where to split the string.
while IFS='=' read -r key val; do
    # Skip over lines containing comments.
    # (Lines starting with '#').
    [ "${key##\#*}" ] || continue

    # '$key' stores the key.
    # '$val' stores the value.
    printf '%s: %s\n' "$key" "$val"

    # Alternatively replacing 'printf' with the following
    # populates variables called '$key' with the value of '$val'.
    #
    # NOTE: I would extend this with a check to ensure 'key' is
    #       a valid variable name.
    # export "$key=$val"
    #
    # Example with error handling:
    # export "$key=$val" 2>/dev/null ||
    #     printf 'warning %s is not a valid variable name\n' "$key"
done < "file"

Get the first N lines of a file

Alternative to the head command.

head() {
    # Usage: head "n" "file"
    while IFS= read -r line; do
        printf '%s\n' "$line"
        i=$((i+1))
        [ "$i" = "$1" ] && return
    done < "$2"

    # 'read' used in a loop will skip over
    # the last line of a file if it does not contain
    # a newline and instead contains EOF.
    #
    # The final line iteration is skipped as 'read'
    # exits with '1' when it hits EOF. 'read' however,
    # still populates the variable.
    #
    # This ensures that the final line is always printed
    # if applicable.
    [ -n "$line" ] && printf %s "$line"
}

Example Usage:

$ head 2 ~/.bashrc
# Prompt
PS1='➜ '

$ head 1 ~/.bashrc
# Prompt

Get the number of lines in a file

Alternative to wc -l.

lines() {
    # Usage: lines "file"

    # '|| [ -n "$line" ]': This ensures that lines
    # ending with EOL instead of a newline are still
    # operated on in the loop.
    #
    # 'read' exits with '1' when it sees EOL and
    # without the added test, the line isn't sent
    # to the loop.
    while IFS= read -r line || [ -n "$line" ]; do
        lines=$((lines+1))
    done < "$1"

    printf '%s\n' "$lines"
}

Example Usage:

$ lines ~/.bashrc
48

Count files or directories in directory

This works by passing the output of the glob to the function and then counting the number of arguments.

count() {
    # Usage: count /path/to/dir/*
    #        count /path/to/dir/*/
    [ -e "$1" ] \
        && printf '%s\n' "$#" \
        || printf '%s\n' 0
}

Example Usage:

# Count all files in dir.
$ count ~/Downloads/*
232

# Count all dirs in dir.
$ count ~/Downloads/*/
45

# Count all jpg files in dir.
$ count ~/Pictures/*.jpg
64

Create an empty file

Alternative to touch.

:>file

# OR (shellcheck warns for this)
>file