Tag: linux

#!/bin/bash
input="/path/to/txt/file"
while IFS= read -r line
do
  echo "$line"
done < "$input"

References
https://www.cyberciti.biz/faq/unix-howto-read-line-by-line-from-file/

Pass arguments through to another program

#!/bin/bash
# print_args.sh
echo "You provided the arguments:" "$@"

# You could pass all arguments to another program like this
# myProgram "$@"

Get the number of arguments passed

#!/bin/bash
echo "You provided $# arguments"

Accessing a specific argument by index

#!/bin/bash
echo "Arg 0: $0"
echo "Arg 1: $1"
echo "Arg 2: $2"

Argument 0 is the name of the script being invoked itself.

Iterating through each argument

#!/bin/bash
for arg in "$@"
do
    echo "$arg"
done

Check arguments for specific value

#!/bin/bash
for arg in "$@"
do
    if [ "$arg" == "--help" ] || [ "$arg" == "-h" ]
    then
        echo "Help argument detected."
    fi
done

References
https://www.devdungeon.com/content/taking-command-line-arguments-bash

echo -n "Some string..."

echo -e "Some string...\c"

printf "a line without trailing linefeed"

printf "a line with trailing linefeed\n"

References
https://stackoverflow.com/questions/11193466/echo-without-newline-in-a-shell-script

Check if File Exist

FILE=/etc/resolv.conf
if test -f "$FILE"; then
    echo "$FILE exist"
fi

FILE=/etc/resolv.conf
if [ -f "$FILE" ]; then
    echo "$FILE exist"
fi

FILE=/etc/resolv.conf
if [[ -f "$FILE" ]]; then
    echo "$FILE exist"
fi

Check if Directory Exist

FILE=/etc/docker
if [ -d "$FILE" ]; then
    echo "$FILE is a directory"
fi

Check if File does Not Exist

FILE=/etc/docker
if [ ! -f "$FILE" ]; then
    echo "$FILE does not exist"
fi

Check if Multiple Files Exist

FILE=/etc/docker
if [ -f /etc/resolv.conf -a -f /etc/hosts ]; then
    echo "$FILE is a directory"
fi

FILE=/etc/docker
if [ -f /etc/resolv.conf && -f /etc/hosts ]; then
    echo "$FILE is a directory"
fi

File test operators

• -f FILE – True if the FILE exists and is a regular file (not a directory or device).
• -G FILE – True if the FILE exists and has the same group as the user running the command.
• -h FILE – True if the FILE exists and is a symbolic link.
• -g FILE – True if the FILE exists and has set-group-id (sgid) flag set.
• -k FILE – True if the FILE exists and has a sticky bit flag set.
• -L FILE – True if the FILE exists and is a symbolic link.
• -O FILE – True if the FILE exists and is owned by the user running the command.
• -p FILE – True if the FILE exists and is a pipe.
• -r FILE – True if the FILE exists and is readable.
• -S FILE – True if the FILE exists and is socket.
• -s FILE – True if the FILE exists and has nonzero size.
• -u FILE – True if the exists and set-user-id (suid) flag is set.
• -w FILE – True if the FILE exists and is writable.
• -x FILE – True if the FILE exists and is executable.

References
https://linuxize.com/post/bash-check-if-file-exists/