Commands by GeckoDH (7)

  • The command `cat file >> file` failes with the following error message: cat: file: input file is output file `tee` is a nice workaround without using any temporary files. Show Sample Output


    0
    cat file | tee >> file
    GeckoDH · 2009-07-30 07:34:03 3
  • Per default, linux/unix shells are configured with a width of 80 characters. If you like to edit a phrase or string on a line with more than 80 characters it might take long to go there (for example a line with 1000 characters and you like to edit the 98th word which is character 598-603). Maybe you might wish to use 78 characters, because if you forward the text via mail and the text will be quoted (2 extra characters at the beginning to the line "> "), you use 80 characters, otherwise 82, which are lame.


    3
    fold -w 78 -s file-to-wrap
    GeckoDH · 2009-05-19 19:33:10 1
  • Ater person A starts his screen-session with `screen`, person B can attach to the srceen of person A with `screen -x`. Good to know, if you need or give support from/to others.


    13
    screen -x
    GeckoDH · 2009-05-19 19:10:52 2
  • You only have to fill in your administrative account and password, and the router FQDN! I recommand to execute this command not over the internet, because there is no encryption (the username and password will be transmitted in plaintext!)


    3
    curl -d 'username=root&password=your-good-password' "http://router/cgi-bin/luci/admin/system/backup?backup=kthxbye" > `date +%Y%d%m`_config_backup.tgz
    GeckoDH · 2009-05-19 11:32:30 1
  • VARNAMES='ID FORENAME LASTNAME ADDRESS CITY PHONE MOBILE MAIL ...' cat customer.csv | while read LINE ; do COUNT=1 for VAR in $VARNAMES ; do eval "${VAR}=`echo $LINE | /usr/bin/awk {'print $'$COUNT''}`" let COUNT=COUNT+1 done done Maybe you have a CSV-File with addresses, where you have to process each contact (one per line, write each value to own variable). Of course you can define every variable, but this way is more simple and faster (to write). VARNAMES includes the variable names. Pay attention: the number of names in VARNAMES have to be the same than in the CSV-file the fields. If the CSV is not seperated with ";", you can set the seperator after the awk-binary with -F"_" for example.


    -1
    VARNAMES='ID FORENAME LASTNAME ADDRESS CITY PHONE MOBILE MAIL' ; cat customer.csv | while read LINE ; do COUNT=1 ; for VAR in $VARNAMES ; do eval "${VAR}=`echo $LINE | /usr/bin/awk {'print $'$COUNT''}`" ; let COUNT=COUNT+1 ; done ; done
    GeckoDH · 2009-05-19 11:23:00 0
  • PRIVATEKEY - Of course the full path to the private key \n HOST - The host where to get the backup \n SOURCE - The directory you wish to backup \n DESTINATION - The destination for the backup on your local machine


    1
    ssh -i $PRIVATEKEY $HOST -C 'cd $SOURCE; tar -cz --numeric-owner .' | tee $DESTINATION/backup.tgz | tar -tz
    GeckoDH · 2009-05-18 20:36:45 0
  • Important to know: a valid date will return 0, otherwise 1!


    2
    date -d2009-05-18 > /dev/null 2>&1 ; echo $?
    GeckoDH · 2009-05-18 20:30:05 0

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Change every instance of OLD to NEW in file FILE
Very quick way to change a word in a file. I use it all the time to change variable names in my PHP scripts (sed -i 's/$oldvar/$newvar/g' index.php)

Forget remembered path locations of previously ran commands
i.e.: Useful if you add ~/bin to your $PATH and you want to override locations of previously ran commands and you don't want to log out and log back in to be able to use them.

Backup your LDAP
Simple way to backup your LDAP entries: put this line on your crontab. The -n switch identifies the dbnum you want to backup (alternatively you can use -b suffix. Check man slapcat for your personal switches)

create a simple version of ls with extended output
create a short alias for 'ls' with multi-column (-C), file type syntax additions (slashes after directories, @ for symlinks, etc... (-F), long format (-l), including hidden directories (all ./, ../, .svn, etc) (-a), show file-system blocks actually in use (-s), human readable file sizes (-h)

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

Send an email from the terminal when job finishes
Might as well include the status code it exited with so you know right away if it failed or not.

Go to the next sibling directory in alphabetical order
Sometimes you have to browse your way through a lot of sub-directories. This command cd to the next sub-directory in alphabetical order. For example, if you have the directories "lectures/01-intro", "lectures/02-basic", "lectures/03-advanced" and so on, and your PWD is "02-basic", it jumps to "03-advanced".

Chage default shell for all users [FreeBSD]
This command will set bash as the default shell for all users in a FreeBSD system.

take execution time of several commands
The last ; is important. example: time { rm -rf /folder/bar && mkdir -p /folder/bar ; echo "done" ; } command is a bash builtin

intercept stdout/stderr of another process


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