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Bash Scripting String

Bash scripting with strings

Mark Lucernas
2020-08-09

String

ANSI String Color Codes

Most Commonly Used

RED="\e[0;31m"
GREEN="\e[0;32m"
BLUE="\e[0;34m"
YELLOW="\e[0;33m"
WHITE="\e[0;37m"
BG_RED="\e[0;101m${expand_bg}"
BG_GREEN="\e[0;102m${expand_bg}"
BG_BLUE="\e[0;104m${expand_bg}"
BG_YELLOW="\e[0;103m${expand_bg}"
BG_EXPAND="\e[K" # Expand any background color horizontally
BO_NC="\e[1m" # No color bold output
UL_NC="\e[4m" # No color underlined output
NC="\e[0m" # Reset to default output color

Sample

  • printf "${RED}ERROR: File does not exists${NC}" – Prints red colored string.
  • echo -e "${RED}ERROR: File does not exists${NC}" – Echo variation. Requires -e flag to enable ’' interpretation in echo command.

More ANSI Color Codes

Regular Colors

BLACK="\e[0;30m"
RED="\e[0;31m"
GREEN="\e[0;32m"
YELLOW="\e[0;33m"
BLUE="\e[0;34m"
PURPLE="\e[0;35m"
CYAN="\e[0;36m"
WHITE="\e[0;37m"

Bold

BO_BLACK="\e[1;30m"
BO_RED="\e[1;31m"
BO_GREEN="\e[1;32m"
BO_YELLOW="\e[1;33m"
BO_BLUE="\e[1;34m"
BO_PURPLE="\e[1;35m"
BO_CYAN="\e[1;36m"
BO_WHITE="\e[1;37m"
BO_NC="\e[1m" # Bold default color

Underline

UL_BLACK="\e[4;30m"
UL_RED="\e[4;31m"
UL_GREEN="\e[4;32m"
UL_YELLOW="\e[4;33m"
UL_BLUE="\e[4;34m"
UL_PURPLE="\e[4;35m"
UL_CYAN="\e[4;36m"
UL_WHITE="\e[4;37m"
UL_NC="\e[4m" # Underlined default color

Background

BG_BLACK="\e[40m"
BG_RED="\e[41m"
BG_GREEN="\e[42m"
BG_YELLOW="\e[43m"
BG_BLUE="\e[44m"
BG_PURPLE="\e[45m"
BG_CYAN="\e[46m"
BG_WHITE="\e[47m"
BG_EXPAND="\e[K" # Expand any background color horizontally

High Intensty

HI_BLACK="\e[0;90m"
HI_RED="\e[0;91m"
HI_GREEN="\e[0;92m"
HI_YELLOW="\e[0;93m"
HI_BLUE="\e[0;94m"
HI_PURPLE="\e[0;95m"
HI_CYAN="\e[0;96m"
HI_WHITE="\e[0;97m"

Bold High Intensty

BO_HI_BLACK="\e[1;90m"
BO_HI_RED="\e[1;91m"
BO_HI_GREEN="\e[1;92m"
BO_HI_YELLOW="\e[1;93m"
BO_HI_BLUE="\e[1;94m"
BO_HI_PURPLE="\e[1;95m"
BO_HI_CYAN="\e[1;96m"
BO_HI_WHITE="\e[1;97m"

High Intensty backgrounds

BG_HI_BLACK="\e[0;100m"
BG_HI_RED="\e[0;101m"
BG_HI_GREEN="\e[0;102m"
BG_HI_YELLOW="\e[0;103m"
BG_HI_BLUE="\e[0;104m"
BG_HI_PURPLE="\e[0;105m"
BG_HI_CYAN="\e[0;106m"
BG_HI_WHITE="\e[0;107m"

Reset to Default

NC="\e[0m"

NOTE: Using ANSI color codes will change all the string onwards. So resetting the string colors with \e[0m at the end of each message is a must.

Ref:

Comparing Strings

Comparing two strings if equal

if [[ "$STRING1" == "$STRING2" ]]; then
    echo "Strings are equal."
else
    echo "Strings are not equal."
fi

if [ "$STRING1" = "$STRING2" ]; then
    echo "Strings are equal."
else
    echo "Strings are not equal."
fi

Comparing if a string contains a substring

VAR='GNU/Linux is an operating system'
if [[ $VAR == *"Linux"* ]]; then
  echo "It's there."
fi

# With regex operator `=~`
VAR='GNU/Linux is an operating system'
if [[ $VAR =~ .*Linux.* ]]; then
  echo "It's there."
fi

NOTE: Using regex operator =~ pattern should not be within quotes (’) or double quotes (")

Check if string is empty

VAR=''
if [[ -z $VAR ]]; then
  echo "String is empty."
fi

VAR='Linuxize'
if [[ ! -n $VAR ]]; then
  echo "String is empty."
fi

NOTE: Type man test for more variable checks

Check if string is empty, newline or spaces

if [[ -n "#(echo "$VARIABLE" | tr -d '\n')" ]]; then
  # Do something if not empty or has new line
fi

#or

if [[ -n "${param// }" ]]; then
  # Do something if not empty or has spaces
fi

Ref:

String Manipulation

Strip single trailing backslash

VALUE=/looks/like/a/path/

echo ${VALUE%/}

Strip all trailing backslashes ‘/’

VALUE=/looks/like/a/path///
TRIMMED=$(echo $VALUE | sed 's,/*$,,')

echo $VALUE $TRIMMED

Ref:


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