Merge pull request #233 from cedric-dufour/master

A few additional cheats

cheat/cheatsheets/apt-get

@@ -23,3 +23,6 @@ apt-get -o Dir::Cache="/path/to/destination/dir/" -o Dir::Cache::archives="./" i
 
 # Show apt-get installed packages.
 grep 'install ' /var/log/dpkg.log
+
+# Silently keep old configuration during batch updates
+apt-get update -o DPkg::Options::='--force-confold' ...

cheat/cheatsheets/awk

@@ -6,3 +6,6 @@ printf '1:2:3' | awk -F ":" '{print $1+$2+$3}'
 
 # print a multiplication table
 seq 9 | sed 'H;g' | awk -v RS='' '{for(i=1;i<=NF;i++)printf("%dx%d=%d%s", i, NR, i*NR, i==NR?"\n":"\t")}'
+
+# Specify output separator character
+printf '1 2 3' | awk 'BEGIN {OFS=":"}; {print $1,$2,$3}'

cheat/cheatsheets/bash

@@ -18,3 +18,10 @@ set -x
 
 # Turn off debugging:
 set +x
+
+# Retrieve N-th piped command exit status
+printf 'foo' | fgrep 'foo' | sed 's/foo/bar/'
+echo ${PIPESTATUS[0]}  # replace 0 with N
+
+# Lock file:
+( set -o noclobber; echo > my.lock ) || echo 'Failed to create lock file'

cheat/cheatsheets/openssl

@@ -19,3 +19,6 @@ openssl x509 -text -noout -in server.crt
 echo | openssl s_client -connect <hostname>:443 2> /dev/null | \
 awk '/-----BEGIN/,/END CERTIFICATE-----/' | \
 openssl x509 -noout -enddate
+
+# Generate Diffie-Hellman parameters:
+openssl dhparam -outform PEM -out dhparams.pem 2048

cheat/cheatsheets/tar

@@ -24,3 +24,8 @@ tar -jtvf /path/to/foo.tgz
 
 # To create a .gz archive and exclude all jpg,gif,... from the tgz
 tar czvf /path/to/foo.tgz --exclude=\*.{jpg,gif,png,wmv,flv,tar.gz,zip} /path/to/foo/
+
+# To use parallel (multi-threaded) implementation of compression algorithms:
+tar -z ... -> tar -Ipigz ...
+tar -j ... -> tar -Ipbzip2 ...
+tar -J ... -> tar -Ipixz ...