BASH tips

Some tips on bash shell. Just a personal documentation

Remove character

sed 's/character //'

for example:

~ $ cat text.txt
Cantarel Bold 14

to get "Cantarel 14" you can use:
~ $ cat text.txt | sed 's/Bold //'
Cantarel 14

Get character separated by something

cut -d 'something' -f column

for example:

~ $ cat text.txt
gtk-font-name=Cantarel, 14

to get "Cantarel, 14" you can use:
~ $ cat text.txt | cut -d '=' -f 2
Cantarel, 14

Get characters on a specific line

awk 'NR==linenumber'

for example:

~ $ cat text.txt
ABCD
EFGH
IJKL

to get "EFGH" you can use:
~ $ cat text.txt | awk 'NR==2'
EFGH

Get characters on a specific column

awk '{print $numbercolumn}'

for example:

~ $ cat text.txt
ABCD EFGH IJKL

to get "EFGH" you can use:
~ $ cat text.txt | awk '{print $2}'
EFGH

Add file or directory on bash script

export PATH="${PATH}:/location"

for example: you want to add some files on your script directory, you can add this line in your bash script

#!/bin/bash
export PATH="${PATH}:/script"

Print character on bash script

#!/bin/bash
cat <<EOF
character
EOF

for example, you can create a new file text.txt then you add this line:

#!/bin/bash
cat <<EOF
Hello World
EOF

then if you run, the result will be:

~ $ bash text.txt
Hello World

Add the colors

tput setaf <0-15>

for example, you can create a new file text.txt then you add this line:

#!/bin/bash
# Add colors
#normal
bla=$(tput setaf 0)
red=$(tput setaf 1)
gre=$(tput setaf 2)
yel=$(tput setaf 3)
blu=$(tput setaf 4)
mag=$(tput setaf 5)
cya=$(tput setaf 6)
whi=$(tput setaf 7)
#bright
bbla=$(tput setaf 8)
bred=$(tput setaf 9)
bgre=$(tput setaf 10)
byel=$(tput setaf 11)
bblu=$(tput setaf 12)
bmag=$(tput setaf 13)
bcya=$(tput setaf 14)
bwhi=$(tput setaf 15)

# Print result
cat <<EOF
$redHello World
EOF

then if you run, the result will be:

~ $ bash text.txt
Hello World (with red color)

Add value option on bash

if [[ $1 = "value" ]]; then
  action
else
  action
fi

for example, in your text.txt you can add this line:

#!/bin/bash
val_1=Hello World
val_2=Hello There

if [[ $1 = "-1" ]]; then
  echo "$(val_1)"
else
  echo "$(val_2)"
fi

then if you run with "-1", the result will be:

~ $ bash text.txt -1
Hello World

if you run without "-1", the result will be:

~ $ bash text.txt
Hello There

Add value option (number) on bash

if [[ $1 =~ ^[0-9]+$ ]]; then
  action
else
  action
fi

for example, in your text.txt you can add this line:

#!/bin/bash

if [[ $1 =~ ^[0-9]+$ ]]; then
  echo "the value is" $1
else
  echo "the value is -"  
fi

then if you run with "number", the result will be:

~ $ bash text.txt 9379
the value is 9379

if you run with "character", the result will be:

~ $ bash text.txt abcd
the value is -

Arithmetic operations

eq=$(($1+$2))
echo $1 + $2 = $eq

for example, in your test.txt you can add this line:

#!/bin/bash

eq=$(($1+$2))
echo $1 + $2 = $eq

then if you run, the result will be:

~ $ bash test.txt 10 7
10 + 7 = 17