Linux BASH

Script dir and name

SCRIPT_NAME=${0##*/}
SCRIPT_PATH="$( dirname -- "${BASH_SOURCE[0]}"; )/"
# TMP_FILE_BASE64="/dev/shm/${SCRIPT_NAME}.data.base64" ...
# TMP_FILE_BASE64="$(mktemp)"

Random Number, String

# numbers (from 1 to 50)
RANDOM_NUMBER=$(echo $(( $RANDOM % 50 + 1 )))
# lowercase + numbers
OPERATION_ID=$(echo $RANDOM | md5sum | head -c 20)
# lowercase + numbers + uppercase
SIMPLE_PASS=$(tr -dc a-zA-Z0-9 < /dev/urandom | head -c 16)

Minutes since EPOCH

MINUTES_SINCE_EPOCH=$(($EPOCHSECONDS/60))

Check if variable is NUMBER

numbers='^[0-9]+$'
if [[ ! ${1} =~ $numbers ]] ; then echo "${SCRIPT_NAME}: [ ${1} ] is NOT a number!" ; return 1 ; fi

Uppercase, Lowercase

str="string"
echo ${str^} nebo echo ${str^^}
str="STRING"
echo ${str,} nebo echo ${str,,}

Substring

Cut chars from the end

FIID_SQL=${FIID_LINE::-1}

Cut chars from the beginning

VAR_WITHOUT_PREFIX=${VAR:4}

Show count of chars from-to particular postion

VAR="123456789" ; echo ${VAR:3:2}

Content that doesn't needs to be escaped

VAR=$(cat << 'EOF'
Single: ' and Double: " quotes variable here.
EOF
)

Count new lines per second in log file

tail -F output.txt | { count=0; old=$(date +%s); while read line; do ((count++)); s=$(date +%s); if [ "$s" -ne "$old" ]; then echo "$count lines per second"; count=0; old=$s; fi; done; }

Redirect all script ouptut (edge case exists) to log

d() {
    date +"%d.%m.%Y - %H:%M:%S"
}

LOGDIR="${SCRIPT_NAME}.logdir/"
if [ ! -d "${LOGDIR}" ] ; then mkdir ${LOGDIR} ; fi
LOGFILE="`date "+%Y_%m_%d"`"
LOG="${LOGDIR}${LOGFILE}"

### LOG TO FILE ONLY
echo "All outputs are redirected to [ ${LOG} ]"
if touch ${LOG}
then
    exec 1>>${LOG}
    exec 2>>${LOG}
else
    echo "[ CRITICAL ] - $(d) - ${SCRIPT_NAME} ERROR: Can't create LOG FILE [ ${LOG} ]. Script FAILED !!!"
    exit 1
fi

### LOG TO FILE and STDOUT
echo "All outputs are redirected to [ ${LOG} ] and standard out"
if touch ${LOG}
then
    exec 3>&1 4>&2
    exec > >(tee -a "${LOG}" >&3) 2> >(tee -a "${LOG}" >&4)
else
    echo "[ CRITICAL ] - $(d) - ${SCRIPT_NAME} : Can't create LOG FILE [ ${LOG} ]. Script FAILED !!!"
    exit 1
fi

Log file lines retention

#!/bin/bash

LOG="/path/to/logfile.log"

ALL_LINES=$(cat ${LOG} | wc -l)
KEEP_LINES="1000"
if [ ${ALL_LINES} -lt ${KEEP_LINES} ] ; then echo "Nothing to delete." ; exit 0 ; fi
DEL_LINES=$((ALL_LINES-KEEP_LINES))

re='^[0-9]+$'
if [[ $DEL_LINES =~ $re ]]
then
    sed -i -e "1,${DEL_LINES}d" "${LOG}"
else
    echo "[ ${DEL_LINES} ] is not a number!"
fi

Redirect only stdout to console and all others to file

{ command | tee /dev/tty; } &> /dev/null

Counting how long a task took

#!/bin/bash

### Record the start time in nanoseconds
start_time=$(date +%s%N)

### TASK (simulated here)
sleep 3.2

### Record the end time in nanoseconds
end_time=$(date +%s%N)
### Calculate the elapsed time in nanoseconds
elapsed_time=$((end_time - start_time))

### Convert nanoseconds to seconds
elapsed_seconds=$((elapsed_time / 1000000000))

echo "Elapsed time: $elapsed_seconds seconds"

Parallel run of several scripts and wait for all to finish

./LVCheck.sh $SRC_LV_DEV "local" &
./LVCheck.sh $DST_LV_DEV "remote" "${USER}@${HOSTNAME}" &
wait $(jobs -p)

Read and process whole line with spaces

while read LINE
do
echo "${LINE}"
done < ${FILE}
### done < <(command)

Date and Time

TIME_MINUTE_AGO=`date --date '-1 min' "+%d%m %H:%M:"`

Fast count of cycles

count=0;
total=0;
for i in $(getSomeNumber)
do
((count++))
total=$(($total+$i))
done

Counting in BASH

!/bin/bash

# Original numbers
a=50.8
b=15.3
# Remove decimal
aa=$(echo ${a%.*})
bb=$(echo ${b%.*})
# Round numbers
aaa=$(printf %.0f $a)
bbb=$(printf %.0f $b)

echo "ORIGINAL $a : $b"
echo "REMOVED DECIMALS $aa : $bb"
echo "ROUNED $aaa : $bbb"

echo " ==== COUNTING ==== "
echo "+ $((aa+bb))"
echo "- $((aa-bb))"
echo "/ $((aa/bb))"
mod=$((aa%bb))
echo "MOD $mod"
echo "DECIMAL $(($mod/$bb))"
echo "> BASH can NOT count with .decimals."

Disable & Enable ALL USB script

Show all devices

for device in $(ls /sys/bus/usb/devices/*/product); do echo $device;cat $device;done

disableUSB.sh

#!/bin/bash

#for device in $(ls /sys/bus/usb/devices/*/product)
for device in $(ls /sys/bus/usb/devices/usb*/product)
do
    DEVICE_ID=$(echo $device | sed "s;.*devices\/\(.*\)\/product.*;\1;")
    echo "DISABLING DEVICE: $DEVICE_ID ($device --- $(cat $device))"
    echo "${DEVICE_ID}" |sudo tee /sys/bus/usb/drivers/usb/unbind
done

enableUSB.sh

#!/bin/bash

for device in $(ls /sys/bus/usb/devices/*/product)
do
    DEVICE_ID=$(echo $device | sed "s;.*devices\/\(.*\)\/product.*;\1;")
    echo "ENABLING DEVICE: $DEVICE_ID ($device --- $(cat $device))"
    echo "${DEVICE_ID}" |sudo tee /sys/bus/usb/drivers/usb/bind
done