Linux check lines in file

Mastering Linux Shell Commands: A Comprehensive Guide to Counting Lines in a File

Learn how to count lines in a file using various shell commands in Linux. Explore wc, awk, sed, grep, and more. Write shell scripts and efficiently handle large files. Get started now!

• Using wc command
• Piping output to wc command
• Using awk or sed command
• Using grep command
• Writing shell scripts
• Other related commands
• Handling whitespace and line continuation characters
• Efficiently working with large files
• Other quick code examples for checking lines in a file in Linux
• Conclusion
• How to read lines from a file in shell script?
• How do I view file lines?
• How do you show lines of text in Linux?
• How can I see the first 20 lines of a file in Linux?

Counting the number of lines in a file is a common task in Linux and can be easily accomplished using shell commands. The most commonly used command for this task is “wc -l [filename]”, but there are other options available as well. In this blog post, we will explore various ways to count lines in a file using shell commands in Linux.

Using wc command

The most common and easiest way to count lines in a file is using the “wc -l [filename]” command. This command also provides options to count words, bytes, and characters in a file. Here is an example of how to use the wc command to count lines in a file:

This will output the number of lines in the “file.txt” file.

Piping output to wc command

Another way to count lines in a file is by piping the output of a program to the “wc -l” command. This can be useful when the program outputs multiple lines of text. Here is an example of how to use the ls command to list all files in a directory and count the number of files:

This will output the number of files in the directory.

Using awk or sed command

The awk and sed commands can also be used to count lines in a file. These commands are more powerful than the wc command and can be used for more complex text processing tasks. Here is an example of how to use the awk command to count lines in a file:

This will output the number of lines in the “file.txt” file.

Here is an example of how to use the sed command to count lines in a file:

This will output the number of lines in the “file.txt” file.

Using grep command

The grep command can be used to search for a specific word or string and count the matching lines. Here is an example of how to use the grep command to count the number of lines that contain the word “example” in a file:

This will output the number of lines that contain the word “example” in the “file.txt” file.

Writing shell scripts

Shell scripts can be written to count lines and words in a file. This can be useful when the task needs to be automated or repeated multiple times. Here is an example of how to write a shell script to count the number of lines in a file:

#!/bin/bash echo -n "Enter filename: " read filename echo "Number of lines: $(wc -l < $filename)" 

This script prompts the user to enter the filename and then counts the number of lines in the file.

Other related commands

Other related commands include head and tail for displaying specific lines of a file and find for searching for files or directories.

The head command can be used to display the first few lines of a file, while tail can be used to display the last few. Here is an example of how to use the head command to display the first 5 lines of a file:

This will output the first 5 lines of the “file.txt” file.

Here is an example of how to use the tail command to display the last 5 lines of a file:

This will output the last 5 lines of the “file.txt” file.

The find command can be used to search for files or directories. Here is an example of how to use the find command to search for all files in a directory that have the “.txt” extension:

find /path/to/directory -name '*.txt' 

This will output a list of all files in the directory that have the “.txt” extension.

Handling whitespace and line continuation characters

It is important to properly handle whitespace and line continuation characters when reading files line by line in shell scripts. Here is an example of how to handle whitespace and line continuation characters in a shell script:

while IFS= read -r line || [ -n "$line" ]; do # process line here done < file.txt 

This script reads each line of the “file.txt” file and processes it, properly handling whitespace and line continuation characters.

Efficiently working with large files

Special techniques may be needed for efficiently working with very large files. One technique is to split the file into smaller chunks and count lines in each chunk. Here is an example of how to split a file into smaller chunks and count lines in each chunk:

split -l 1000000 file.txt file_part_ 

This will split the “file.txt” file into smaller files of 1,000,000 lines each, starting with the filename “file_part_”.

Another technique is to use specialized tools like Hadoop or Spark to efficiently process the data.

Other quick code examples for checking lines in a file in Linux

In Shell as proof, linux get lines in file

In Shell , show specific lines in file linux

$ cat sample_file.txt | awk 'NR==9' #[Prints 9th line]

Conclusion

Counting the number of lines in a file is a common task in Linux and can be easily accomplished using shell commands. The most commonly used command for this task is “wc -l [filename]”, but there are other options available as well. We explored various ways to count lines in a file using shell commands, including the wc, awk, sed, and grep commands, as well as writing shell scripts. We also discussed related commands like head, tail, and find, and important considerations like handling whitespace and line continuation characters and efficiently working with large files. With this comprehensive guide, you should be well-equipped to count lines in a file using shell commands in Linux.

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How to find lines containing a string in linux [closed]

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.

This question does not appear to be about a specific programming problem, a software algorithm, or software tools primarily used by programmers. If you believe the question would be on-topic on another Stack Exchange site, you can leave a comment to explain where the question may be able to be answered.

I have a file in Linux, I would like to display lines which contain a specific string in that file, how to do this?

5 Answers 5

The usual way to do this is with grep , which uses a regex pattern to match lines:

Each line which matches the pattern will be output. If you want to search for fixed strings only, use grep -F 'pattern' file . fgrep is shorthand for grep -F .

addition grep -rn 'string' /path/ if you want to search a string in a folder in which file including and line number

Besides grep , you can also use other utilities such as awk or sed

Here is a few examples. Let say you want to search for a string is in the file named GPL .

Your sample file

$ cat -n GPL 1 The GNU General Public License is a free, copyleft license for 2 The licenses for most software and other practical works are designed 3 the GNU General Public License is intended to guarantee your freedom to 4 GNU General Public License for most of our software; 

$ grep is GPL The GNU General Public License is a free, copyleft license for the GNU General Public License is intended to guarantee your freedom to 

$ awk /is/ GPL The GNU General Public License is a free, copyleft license for the GNU General Public License is intended to guarantee your freedom to 

$ sed -n '/is/p' GPL The GNU General Public License is a free, copyleft license for the GNU General Public License is intended to guarantee your freedom to 

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How to check if a file contains a specific string using Bash

I want to check if a file contains a specific string or not in bash. I used this script, but it doesn't work:

 if [[ 'grep 'SomeString' $File' ]];then # Some Actions fi 

11 Answers 11

if grep -q SomeString "$File"; then Some Actions # SomeString was found fi 

You don't need [[ ]] here. Just run the command directly. Add -q option when you don't need the string displayed when it was found.

The grep command returns 0 or 1 in the exit code depending on the result of search. 0 if something was found; 1 otherwise.

$ echo hello | grep hi ; echo $? 1 $ echo hello | grep he ; echo $? hello 0 $ echo hello | grep -q he ; echo $? 0 

You can specify commands as an condition of if . If the command returns 0 in its exitcode that means that the condition is true; otherwise false.

$ if /bin/true; then echo that is true; fi that is true $ if /bin/false; then echo that is true; fi $ 

As you can see you run here the programs directly. No additional [] or [[]] .

if SomeString contains regex special characters (like . ) you might get unexpected results. It's safer to always use fgrep (or grep -F ) (unless you really need a regex, in which case egrep (or grep -E ) is probably the best choice)

The example if example is incorrect, as it only checks if the exit code was non-0. If any error happens, like the file can't be read, the exit code is also non-0. So you have to do something like ec=$? , and check if it's 0 (found), then if it's 1 (not found), and then if it's something else (fail).

In case if you want to check whether file does not contain a specific string, you can do it as follows.

if ! grep -q SomeString "$File"; then Some Actions # SomeString was not found fi 

Suppose you have several stings in an "input file" that you want to test. Can you combine your solution with cat (and xargs )? Or do you need a for loop?

Is this possible to compare lines from a variable to lines from a text file? Is there a way to set multiple lines to compare instead of SomeString ?

In addition to other answers, which told you how to do what you wanted, I try to explain what was wrong (which is what you wanted.

In Bash, if is to be followed with a command. If the exit code of this command is equal to 0, then the then part is executed, else the else part if any is executed.

You can do that with any command as explained in other answers: if /bin/true; then . ; fi

[[ is an internal bash command dedicated to some tests, like file existence, variable comparisons. Similarly [ is an external command (it is located typically in /usr/bin/[ ) that performs roughly the same tests but needs ] as a final argument, which is why ] must be padded with a space on the left, which is not the case with ]] .

Another thing is the way you quote things. In bash, there is only one case where pairs of quotes do nest, it is "$(command "argument")" . But in 'grep 'SomeString' $File' you have only one word, because 'grep ' is a quoted unit, which is concatenated with SomeString and then again concatenated with ' $File' . The variable $File is not even replaced with its value because of the use of single quotes. The proper way to do that is grep 'SomeString' "$File" .

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