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@ -545,7 +545,7 @@ sed -i '$ s/.$//' filename
##### Add string to beginning of file (e.g. "\[") ##### Add string to beginning of file (e.g. "\[")
```bash ```bash
sed -i '1s/^/[/' filename sed -i '1s/^/[/' file
``` ```
##### Add string at certain line number (e.g. add 'something' to line 1 and line 3) ##### Add string at certain line number (e.g. add 'something' to line 1 and line 3)
@ -692,7 +692,7 @@ sed '$ s/.$//'
##### Insert character at specified position of file (e.g. AAAAAA --> AAA#AAA) ##### Insert character at specified position of file (e.g. AAAAAA --> AAA#AAA)
```bash ```bash
sed -r -e 's/^.{3}/&#/' filename sed -r -e 's/^.{3}/&#/' file
``` ```
@ -747,7 +747,7 @@ awk -v N=7 '{print}/bbo/&& --N<=0 {exit}'
##### Print filename and last line of all files in directory ##### Print filename and last line of all files in directory
```bash ```bash
ls|xargs -n1 -I file awk '{s=$0};END{print FILENAME,s}' filename ls|xargs -n1 -I file awk '{s=$0};END{print FILENAME,s}' file
``` ```
##### Add string to the beginning of a column (e.g add "chr" to column $3) ##### Add string to the beginning of a column (e.g add "chr" to column $3)
@ -757,12 +757,12 @@ awk 'BEGIN{OFS="\t"}$3="chr"$3'
##### Remove lines with string (e.g. 'bbo') ##### Remove lines with string (e.g. 'bbo')
```bash ```bash
awk '!/bbo/' filename awk '!/bbo/' file
``` ```
##### Remove last column ##### Remove last column
```bash ```bash
awk 'NF{NF-=1};1' filename awk 'NF{NF-=1};1' file
``` ```
##### Usage and meaning of NR and FNR ##### Usage and meaning of NR and FNR
@ -827,7 +827,7 @@ awk '{printf("%s\t%s\n",NR,$0)}'
# David cat # David cat
# David dog # David dog
awk '{split($2,a,",");for(i in a)print $1"\t"a[i]}' filename awk '{split($2,a,",");for(i in a)print $1"\t"a[i]}' file
# Detail here:　http://stackoverflow.com/questions/33408762/bash-turning-single-comma-separated-column-into-multi-line-string # Detail here:　http://stackoverflow.com/questions/33408762/bash-turning-single-comma-separated-column-into-multi-line-string
``` ```
@ -941,7 +941,7 @@ find /dir/to/A -type f -name "*.py" -print 0| xargs -0 -r -I file cp -v -p file
##### With sed ##### With sed
```bash ```bash
ls |xargs -n1 -I file sed -i '/^Pos/d' filename ls |xargs -n1 -I file sed -i '/^Pos/d' file
``` ```
##### Add the file name to the first line of file ##### Add the file name to the first line of file
@ -1052,10 +1052,9 @@ else
echo >&2 "Fatal error. This script requires mydir." echo >&2 "Fatal error. This script requires mydir."
fi fi
# Check if a variable is null # if variable is null
if [ -z "$var" ]; then echo "NULL"; else echo "Not NULL"; fi if [ ! -s "myvariable" ]; then echo -e "variable is null!" ; fi
# or #True of the length if "STRING" is zero.
[ -z "$var" ] && echo "NULL"
# Using test command (same as []), to test if the length of variable is nonzero # Using test command (same as []), to test if the length of variable is nonzero
test -n "$myvariable" && echo myvariable is "$myvariable" || echo myvariable is not set test -n "$myvariable" && echo myvariable is "$myvariable" || echo myvariable is not set
@ -1552,17 +1551,9 @@ stat filename.txt
ps aux ps aux
``` ```
##### List processes by top memory usage
```bash
ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
```
##### Display a tree of processes ##### Display a tree of processes
```bash ```bash
pstree pstree
# or
ps aux --forest
``` ```
##### Find maximum number of processes ##### Find maximum number of processes
@ -1968,7 +1959,7 @@ ldconfig -p
ldd /bin/ls ldd /bin/ls
``` ```
##### Check the most recent login of all users ##### Check user login
```bash ```bash
lastlog lastlog
``` ```
@ -2281,12 +2272,7 @@ sar -f /var/log/sa/sa31|tail
journalctl --file ./log/journal/a90c18f62af546ccba02fa3734f00a04/system.journal --since "2020-02-11 00:00:00" journalctl --file ./log/journal/a90c18f62af546ccba02fa3734f00a04/system.journal --since "2020-02-11 00:00:00"
``` ```
##### Show a listing of last logged in users ##### Show a listing of last logged in users.
```bash
last
```
##### Show a listing of unsuccessful (bad) login attempts
```bash ```bash
lastb lastb
``` ```
@ -2464,11 +2450,6 @@ dig +short www.example.com
host www.example.com host www.example.com
``` ```
##### Check public IP address
```bash
curl http://checkip.amazonaws.com
```
##### Get DNS TXT record a of domain ##### Get DNS TXT record a of domain
```bash ```bash
dig -t txt www.example.com dig -t txt www.example.com
@ -2509,7 +2490,7 @@ $ sudo nc -l 80
##### Check which ports are listening for TCP connections from the network ##### Check which ports are listening for TCP connections from the network
```bash ```bash
# note that some companies might not like you using nmap #notice that some companies might not like you using nmap
nmap -sT -O localhost nmap -sT -O localhost
# check port 0-65535 # check port 0-65535
@ -2517,7 +2498,7 @@ nmap -p0-65535 localhost
``` ```
##### Check if a host is up and scan for open ports, also skip host discovery. ##### Check if a host is up and scan for open ports, also skip host discovery.
```bash ```bash
# skips checking if the host is alive. this may sometimes cause a false positive, stopping the scan. #skips checking if the host is alive which may sometimes cause a false positive and stop the scan.
$ nmap google.com -Pn $ nmap google.com -Pn
# Example output: # Example output:
@ -2539,7 +2520,7 @@ $ nmap -A -T4 scanme.nmap.org
# -A to enable OS and version detection, script scanning, and traceroute; -T4 for faster execution # -A to enable OS and version detection, script scanning, and traceroute; -T4 for faster execution
``` ```
##### Look up website information (e.g. name server), searches for an object in a RFC 3912 database ##### Look up website information (e.g. name server), searches for an object in a RFC 3912 database.
```bash ```bash
whois google.com whois google.com
``` ```
@ -2549,7 +2530,7 @@ whois google.com
openssl s_client -showcerts -connect www.example.com:443 openssl s_client -showcerts -connect www.example.com:443
``` ```
##### Display network interfaces and their associated IP addresses ##### Display IP address
```bash ```bash
ip a ip a
``` ```
@ -2609,10 +2590,6 @@ curl -I http://example.com/
# Accept-Ranges: bytes # Accept-Ranges: bytes
# Vary: Accept-Encoding # Vary: Accept-Encoding
``` ```
##### Find out the time spent between request and response
```
curl -v -o /dev/null -s -w 'Total: %{time_total}s\n' google.com
```
##### Find out the http status code of a URL ##### Find out the http status code of a URL
```bash ```bash
@ -2893,7 +2870,7 @@ echo -e 'text here \c'
##### View first 50 characters of file ##### View first 50 characters of file
```bash ```bash
head -c 50 filename head -c 50 file
``` ```
##### Cut and get last column of a file ##### Cut and get last column of a file
@ -2931,11 +2908,6 @@ cat >>myfile
let me add sth here let me add sth here
# exit with ctrl+d # exit with ctrl+d
# or
cat << EoF >> filename
> add something here
> EoF
# or using tee # or using tee
tee -a myfile tee -a myfile
let me add sth else here let me add sth else here
@ -2954,7 +2926,7 @@ echo 'hihi' >>filename
##### Working with json data ##### Working with json data
```bash ```bash
# Install the useful jq package #install the useful jq package
#sudo apt-get install jq #sudo apt-get install jq
#e.g. to get all the values of the 'url' key, simply pipe the json to the following jq command(you can use .[]. to select inner json, i.e jq '.[].url') #e.g. to get all the values of the 'url' key, simply pipe the json to the following jq command(you can use .[]. to select inner json, i.e jq '.[].url')
cat file.json | jq '.url' cat file.json | jq '.url'
@ -3029,7 +3001,7 @@ while read a b; do yes $b |head -n $a ; done <test.txt
## Others ## Others
[[back to top](#handy-bash-one-liners)] [[back to top](#handy-bash-one-liners)]
##### Describe the format and characteristics of image files ##### Describe the format and characteristics of image files.
```bash ```bash
identify myimage.png identify myimage.png
#myimage.png PNG 1049x747 1049x747+0+0 8-bit sRGB 1.006MB 0.000u 0:00.000 #myimage.png PNG 1049x747 1049x747+0+0 8-bit sRGB 1.006MB 0.000u 0:00.000
@ -3305,12 +3277,6 @@ scp -r directoryname user@ip:/path/to/send
# :(){:|:&};: # :(){:|:&};:
``` ```
##### Trigger kernel crash
```bash
# Don't try this at home!
echo c > /proc/sysrq-trigger
```
##### Use the last argument ##### Use the last argument
```bash ```bash
!$ !$