Replace on the command line
# sample replace linux command line. (command comes with mysql installation)
# ie replace a b -- filelist
# -v = verbose
# a, b = strings from,to can be quoted. if double, escape things like $ with a backslash
replace -v "string to replace; \$a = \$b " 'string to insert; $c = $d ' -- *
TAR & GZIP
# to create a compressed tar acrchive
tar -cvzf foo.tar.gz *.cc *.h
# To untar/unzip
tar -xvzf filename
x = ie reverse: untar instead of tar
v = verbose
z = handle compression
f = followed by filename
To grep recursively thru all subfolders etc
grep -r 'search stuff' *
-r = recursive
if a wild isn't used as filepattern, then it appears to fail to act recursively
To grep very widely try:
locate exim | xargs grep -in 'blackhole'
ie find all files with 'exim' in their path and grep for blackhole within them!
best to check how many lines first! (ie do a locate first then the whole lot!
Or to search within a particular folder (and it's sub folders)
find -iname '*exim*' | xargs grep -in 'blackhole'
Setting up certificates for SSH, RSYNC and SCP
On master box: (ie the computer that originates an rsync command)
ssh-keygen -t rsa
don't use a passphrase , so hit enter and accept defaults
this will create files in the .ssh directory:
Send the public key to the slave box using scp:
scp id_rsa.pub email@example.com:~/id_rsa.pub
On the slave box, logged in as someuser
touch authorized_keys # creates files miss this step if already exists!
chmod 600 authorized_keys
cat ../id_rsa.pub >>authorized_keys
On master box test with
ssh -2 -v firstname.lastname@example.org
[updated Jan 2017 to use rsa instead of dsa keys. Dsa now deprecated.]
Check the first line of each CGI script
When updating my php handing for cgi I needed to confirm the first line was changed from
So how to view all the first lines without lots of work?
(starting from the document root for the site)
1. Create a list of all cgi files
find ./ -name '*.cgi' >cgilist.txt
2. Use head to display the first 18 characters of each file
xargs --arg-file=cgilist.txt head -c 18
I opt to display the first 18 characters instead of the first line to avoid problems with binary files.