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Tue, Nov 11, 2014 11:06 pm

MySQL service not running on CentOS 7 system

When I issued the mysql command on a CentOS 7 system, I received the error message below:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111)

It took me awhile to figure out that since I was using MariaDB, a fork of MySQL, that I needed to enter the following 3 commands to enable, run, and secure the MariaDB service.

systemctl start mariadb.service
systemctl enable mariadb.service

[ More Info ]

[/software/database/mysql] permanent link

Tue, Nov 11, 2014 5:26 pm

Checking the creation and modified times for files with python

If I want to display each line in a file with a python script and at the end of the output print the number of lines in the file, I can use the python code below:
filename = raw_input("Enter file name: ")
with open(filename) as input_file:
    for i, line in enumerate(input_file):
        print line,
print "{0} line(s) printed".format(i+1)

The script will prompt me for the name of the file to be checked and will loop through that file displaying each line from it, printing the total number of lines at the end of the file.

The comma after the print line statement prevents a newline from being printed, so each file name will be printed immediately below the preceding one without a blank line between them. If the comma was not there, a blank line would be printed between each line containing a file name.

The {0} references the first positional argument in the format statement, which in the case above refers to "i+1". The .format(value) at the end of the line tells python how to format the output. So the count of the number of lines in the file, which will be i plus 1, will be printed after the for loop completes.

If each line in the file is a directory path and file name, e.g.,:


then I can use import os.path, time to import modules that that will will allow me to obtain the time stamps for the files.

import os.path, time

filename = raw_input("Enter file name: ")
with open(filename) as input_file:
    for i, line in enumerate(input_file):
        print line,
        line = line.rstrip('\r\n')
        print "last modified: %s" % time.ctime(os.path.getmtime(line)),
        print "created: %s" % time.ctime(os.path.getctime(line))
print "{0} line(s) printed".format(i+1)

Since the input file was created on a Linux system each line ends with a newline character, which is represented by "\n". So I have to strip off the trailing newline at the end of each file name in the input file with the rstrip function. If the input file was created on a Windows system, I would have to strip off a carriage return, which is represented by "\r". By using rstrip('\r\n'), any carriage return or newline characters will be stripped from the end of each line in the input file, so the script will work on Mac OS, Mac OS X, Microsoft Windows, or Unix/Linux systems.

I see output such as the following when I run the python script:

$ python
Enter file name: checkfiles2_php.txt
last modified: Mon Jan  9 15:45:00 2006 created: Tue Oct 14 10:21:03 2014
last modified: Wed Jan 11 23:42:00 2006 created: Tue Oct 14 10:21:03 2014
last modified: Sat Aug 11 17:22:14 2012 created: Tue Oct 14 10:21:05 2014
last modified: Sun Oct  6 13:30:27 2013 created: Tue Oct 14 10:21:12 2014

The creation times displayed above are the time I copied files from an old drive to a new drive.


  1. python looping through input file
    Date: July 30, 2013
  2. Python trailing comma after print executes next instruction
    Date: October 24, 2010
  3. 6.1. string — Common string operations
    Python 3.4.2 documentation
  4. Python string formatting: % vs. .format
    Date: February 22, 2011
  5. How can I remove (chomp) a newline in Python?
    Date: November 8, 2008
  6. How to get file creation & modification date/times in Python?
    Date: October 25, 2008

[/languages/python] permanent link

Tue, Nov 11, 2014 5:15 pm

Finding a particular string in files

On a Linux/Unix or Mac OS X system, you can use the find and grep commands to search for a specific text string in files. E.g., if you wished to search all files with a ".php" file extension for the occurrence of the word "noindex", you could use the following command:

find . -name "*.php" -exec grep "noindex" {} /dev/null \;

Since "*" has a special meaning for the shell, you will need to include it within quotes or precede it with the backslash escape character as shown below:

$ find . -type f -name \*.php -exec grep -l "noindex" {} \;

If I wished to search all files, not just those ending with ".php", I can use a command similar to the following one.

find . -type f -exec grep "noindex" {} \;

The -type f instructs find to only check regular files and not other objects such as directory names.

If I want to send the results to an output file, I could just append a >outputfile_name to the end of the line, but that will also produce output indicating that the output file itself is being checked.

$ find . -type f -exec grep "noindex" {} \; >checkfiles.txt
grep: input file ‘./checkfiles.txt’ is also the output

To avoid that issue, you can use the --exclude argument.

$ find . -type f -exec grep -l --exclude checkfiles.txt "noindex" {} \; >checkfiles.txt

I can also use just the grep command, as shown belown:

$ grep -rwl . -e "noindex" --include=\*.php

The -r option tells grep to search recursively; the "." is indicating that the search should be started in the current directory. The -w indicates that I want exact word matches, e.g., " noindex ", not "nonindex" or "noindexes". The -l option indicates that I don't want to see the lines on which the word occurs, just the file names for those files in which it is found. The -e option provides the pattern that grep should search on and the --include option tells grep which files it should search within.

       -r, --recursive
              Read  all  files  under  each  directory, recursively, following
              symbolic links only if they are on the command  line.   This  is
              equivalent to the -d recurse option.

       -w, --word-regexp
              Select  only  those  lines  containing  matches  that form whole
              words.  The test is that the matching substring must  either  be
              at  the  beginning  of  the  line,  or  preceded  by  a non-word
              constituent character.  Similarly, it must be either at the  end
              of  the  line  or  followed by a non-word constituent character.
              Word-constituent  characters  are  letters,  digits,   and   the

       -l, --files-with-matches
              Suppress  normal  output;  instead  print the name of each input
              file from which output would normally have  been  printed.   The
              scanning  will  stop  on  the  first match.  (-l is specified by

      -e PATTERN, --regexp=PATTERN
              Use  PATTERN  as  the  pattern.   This  can  be  used to specify
              multiple search patterns, or to protect a pattern beginning with
              a hyphen (-).  (-e is specified by POSIX.)

              Search only files whose base name matches GLOB  (using  wildcard
              matching as described under --exclude).


  1. Finding a String with a Recursive Grep
    Date: March 10, 2007
    MoonPoint Support
  2. How can I use grep to show just filenames (no in-line matches) on linux?
    Date: July 9, 2011

[/os/unix/commands] permanent link

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