cmd line tips

Command line
------------
# Get the first argument of the previous command. This is a readline thing.
[Ctrl]+[Alt]+Y


File
-----
Count the number of commas (,) in a text file: .tr -cd , < file.txt | wc -m #
grep -n "search term" -r . | cut -d ":" -f 1 # extract the paths of a grep output and use them further...
find . -name '*.pdf' -exec pdftotext {} - \; | grep "search term" # grep multiple pdf files
file .* * # List all files in the current directory, and describe their contents.

mkdir ". " && cd ". " && touch FILE # put as many spaces as you want after dot. Hiding files in Linux

Encryption
----------
echo "Uryyb jbeyq" | tr '[A-Za-z]' '[N-ZA-Mn-za-m]' # Perform ROT13 on a string.




Password
--------
dd if=/dev/random bs=16 count=1 2>/dev/null | base64 | sed 's/=//g' # Generate a secure password with 128 bits of entropy.


Edit file
---------
sed '/^\#/d' in_file > out_file # get rid of lines starting with # (aka comments)


Networking
----------
tar -cz folder | ssh username@destinationhostname "cat >output.tgz" | Archive 'folder' onto a different computer.

Web
---


Curl
----
# see where a URL shortener points
curl -s -D - -o /dev/null http://bit.ly/frXy3V  | grep -i ^location:
curl -s "http://download.finance.yahoo.com/d/quotes.csv?s=aapl&f=l1 …" # View current stock price for AAPL
curl -LIN "$URL" # See HTTP response headers and any redirects for $URL


Wget
----
wget -O /dev/null http://speedtest.wdc01.softlayer\.com/downloads/test10.zip # Check broadband speed
wget -r -l 1 -A pdf ftp://ftpserver/pub/documents/ # download all .pdf files from an ftp server



Desktop
-------
# site shot from command line. By
xvfb-run --server-args="-screen 0, 1024x768x24" cutycapt --url=http://url --out=image.png



Networking
----------
# Show the network calls of the ping command.
strace -s 200 -e trace=network -f ping -c1 4.2.2.2

# route port 80 to default or custom port
ltunnel(){ port=3000; sudo ssh -L 80:localhost:${1-$port} $(whoami)@localhost }


Netcat
------
nc -z example\.com 22 # Check if port 22 is listening on http://example.com


Logfiles
--------

tail error_log continuously and add extra newline. May help with readability when lines are long.
tail -f error_log |awk '{print $0 "\n"}'

# sort and rank who is using sudo
egrep -o "sudo:\s+\S+\s+:" /var/log/secure | sort | uniq -c | sort -g


OpenSSL
-------
openssl enc -aes-256-cbc -salt -in yourfile -out yourfile.enc # Encrypt yourfile with a password without the need for gpg.


Apache
-------
# Only view the active configuration in a heavily commented httpd.conf file.
egrep -v "(^#|^\ *$)" httpd.conf | less