Manipulation of text by programs, scripts, etc.

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172
votes
5answers
60k views

Why is printf better than echo?

I have heard that printf is better than echo and I can recall only one instance from my experience where I had to use printf because echo didn't work for feeding some text into some program on RHEL ...
57
votes
8answers
60k views

How to add a newline to the end of a file?

Using version control systems I get annoyed at the noise when the diff says No newline at end of file. So I was wondering: How to add a newline at the end of a file to get rid off those messages?
53
votes
11answers
25k views

how do you sort du output by size?

How do you sort du -sh /dir/* by size? I read one site that said use | sort -n but that's obviously not right. Here's an example that is wrong. [~]# du -sh /var/* | sort -n 0 /var/mail 1.2M ...
46
votes
2answers
69k views

How can I replace a string in a file(s)?

Replacing strings in files based on certain search criteria is a very common task. How can I replace string foo with bar in all files in the current directory? do the same recursively for sub ...
43
votes
4answers
25k views

Can grep output only specified groupings that match?

Say I have a file: # file: 'test.txt' foobar bash 1 bash foobar happy foobar I only want to know what words appear after "foobar", so I can use this regex: "foobar \(\w\+\)" The parenthesis ...
42
votes
8answers
57k views

Looping through files with spaces in the names?

I wrote the following script to diff the outputs of two directores with all the same files in them as such: #!/bin/bash for file in `find . -name "*.csv"` do echo "file = $file"; diff ...
41
votes
5answers
26k views

How to remove duplicate lines inside a text file?

A huge (up to 2 GiB) text file of mine contains about 100 exact duplicates of every line in it (useless in my case, as the file is a CSV-like data table). What I need is to remove all the repetitions ...
40
votes
4answers
20k views

Why is `while IFS= read` used so often, instead of `IFS=; while read..`?

It seems that normal practice would put the setting of IFS outside the while loop in order to not repeat setting it for each iteration... Is this just a habitual "monkey see, monkey do" style, as it ...
34
votes
3answers
2k views

Why is using a shell loop to process text considered bad practice?

Is using a while loop to process text generally considered bad practice in POSIX shells? As Stéphane Chazelas pointed out, some of the reasons for not using shell loop are conceptual, reliability, ...
34
votes
8answers
6k views

Linux tools to treat files as sets and perform set operations on them

Does anyone know of any linux tool specifically designed to treat files as sets and perform set operations on them? Like difference, intersection, etc?
32
votes
4answers
8k views

How can I wrap text at a certain column size?

I know that I can use something like cat test.txt | pr -w 80 to wrap lines to 80 characters wide, but that puts a lot of space on the top and bottom of the printed lines and it does not work right on ...
28
votes
7answers
6k views

Is there a way to modify a file in-place?

I have a fairly large file (35Gb), and I would like to filter this file in situ (i.e. I don't have enough disk space for another file), specifically I want to grep and ignore some patterns — is there ...
27
votes
14answers
59k views

How to count the number of a specific character in each line?

I was wondering how to count the number of a specific character in each line by some text processing utilities? For example, to count " in each line of the following text "hello!" Thank you! The ...
27
votes
3answers
12k views

How can I make iconv replace the input file with the converted output?

I have a bash script which enumerates through every *.php file in a directory and applies iconv to it. This gets output in STDOUT. Since adding the -o parameter ( in my experience ) actually writes ...
26
votes
5answers
10k views

How to obtain inverse behavior for `tail` and `head`?

Is there a way to head/tail a document and get the reverse output; because you don't know how many lines there are in a document? I.e. I just want to get everything but the first 2 lines of foo.txt ...
22
votes
6answers
10k views

sort but keep header line at the top

I am getting output from a program that first produces one line that is a bunch of column headers, and then a bunch of lines of data. I want to cut various columns of this output and view it sorted ...
22
votes
10answers
6k views

How can I write to the second line of a file from the command line?

I have an external program that produces an output file (largish, 20K lines possible). I need to insert a new line between the existing line 1 and line 2. I've been looking at awk and sed - I use ...
21
votes
3answers
38k views

How to merge all (text) files in a directory into one?

I've got 14 files all being parts of one text. I'd like to merge them into one. How to do that?
21
votes
7answers
6k views

A standard tool to convert a byte-count into human KiB MiB etc; like du, ls1

Is there a standard tool which converts an integer count of Bytes into a human-readable count of the largest possible unit-size, while keeping the numeric value between 1.00 and 1023.99 ? I have my ...
20
votes
5answers
7k views

echo a file without the first and last lines

Is there a simple way I can echo a file, skipping the first and last lines? I was looking at piping from head into tail, but for those it seems like I would have to know the total lines from the ...
20
votes
11answers
9k views

Is there a robust command line tool for processing csv files?

I work with CSV files and sometimes need to quickly check the contents of a row or column from the command line. In many cases cut, head, tail, and friends will do the job; however, cut cannot easily ...
20
votes
6answers
30k views

combine text files column-wise

I have two text files. The first one has content: Languages Recursively enumerable Regular while the second one has content: Minimal automaton Turing machine Finite I want to combine them into ...
20
votes
2answers
932 views

Is there a reason why ls does not have a --zero or -0 option

This question was prompted by questions about ls' -1 option and the recurring tendency of people to ask question and answers that includes processing the output of ls. This reuse of the output ls ...
20
votes
6answers
10k views

Removing control chars (including console codes / colours) from script output

I can use the "script" command to record an interactive session at the command line. However, this includes all control characters and colour codes. I can remove control characters (like backspace) ...
20
votes
5answers
11k views

Filtering invalid utf8

I have a text file in an unknown or mixed encoding. I want to see the lines that contain a byte sequence that is not valid UTF-8 (by piping the text file into some program). Equivalently, I want to ...
20
votes
1answer
1k views

How to implement a horizontal cat? [duplicate]

Standard cat concatenates files line by line (row by row, if you will). I find myself needing a horizontal cat command more and more often recently; i.e. a command that takes a list of files and ...
20
votes
5answers
5k views

Command line friendly spreadsheets

Does such a thing exist? Text-based spreadsheets that display well in a CLI environment. I'm aware that I could cat foobar.csvand do as I please, but it isn't particularly practical or attractive. I ...
19
votes
2answers
1k views

Pipes, how do data flow in a pipeline?

I don't understand how the data flows in the pipeline and hope someone could clarify what is going on there. I thought a pipeline of commands processes files (text, arrays of strings) in line by line ...
18
votes
3answers
2k views

Unix command to check if any two lines in a file are same?

Is there a unix command that can check if any two lines in a file are the same? For e.g. Consider a file sentences.txt This is sentence X This is sentence Y This is sentence Z This is sentence X ...
18
votes
5answers
21k views

Shell: How to read the bytes of a binary file and print as hexadecimal?

In shell, how can I read the bytes of a binary file I have, and print the output as hexadecimal numbers?
18
votes
4answers
7k views

How to get only the unique results without having to sort data?

$ cat data.txt aaaaaa aaaaaa cccccc aaaaaa aaaaaa bbbbbb $ cat data.txt | uniq aaaaaa cccccc aaaaaa bbbbbb $ cat data.txt | sort | uniq aaaaaa bbbbbb cccccc $ The result that I need is to display ...
17
votes
9answers
2k views

Grep lines but let the first line through [duplicate]

Consider the following output from df. Filesystem Size Used Avail Use% Mounted on /dev/sda1 23G 6.1G 16G 29% / udev 10M 0 10M 0% /dev tmpfs 397M 420K ...
17
votes
8answers
23k views

Command to display first few and last few lines of a file

I have a file with many rows, and each row has a timestamp at the starting, like [Thread-3] (21/09/12 06:17:38:672) logged message from code..... So, I frequently check 2 things from this log file. ...
16
votes
3answers
18k views

How can I find out how many lines a text file contains without viewing it?

How can I find how many lines a text file contains without opening the file in an editor or a viewer application? Is there a handy Unix console command to see the number?
16
votes
2answers
4k views

Horizontal file concatenation

Is there a Linux command like cat that joins files with the same number of lines horizontally?
16
votes
3answers
12k views

How do I remove certain lines (using line numbers) in a file?

There are specific lines that I want to remove from a file. Let's say it's line 20-37 and then line 45. How would I do that without specifying the content of those lines?
16
votes
3answers
930 views

Looking for an old classical Unix toolkit textbook

I am looking for a book about the Unix command-line toolkit (sh, grep, sed, awk, cut, etc.) that I read some time ago. It was an excellent book, but I totally forgot its name. The great thing about ...
15
votes
2answers
3k views

sort inplace - like sed --in-place - exists?

Am I blind or is there no option like --in-place for sort? In order to save results to the input file, sed uses -i (--in-place). Redirecting the output of sort to the input file sort < f > f ...
15
votes
2answers
2k views

How can I count the number of different characters in a file?

I would need a program, that outputs the number of the different characters in a file. Example: > stats testfile ' ': 207 'e': 186 'n': 102 Exists any tool, that do this?
15
votes
3answers
17k views

How to find unmatched brackets in a text file?

Today I learned that I can use perl -c filename to find unmatched curly brackets {} in arbitrary files, not necessarily Perl scripts. The problem is, it doesn't work with other types of brackets () [] ...
14
votes
14answers
3k views

How to read an IP address backwards?

If we have this string (IP address): 192.168.1.1 How can I derive the (DNS reverse record form) from this string, so it will be shown like 1.1.168.192.in-addr.arpa using a shell script?
14
votes
4answers
17k views

Delete last line from the file

I use sed to quickly delete lines with specific position as sed '1d' sed '5d' But, what if I want to delete the last line of the file and I don't know the count of lines (I know I can get that ...
14
votes
10answers
3k views

There must be a better way to replace single newlines only?

I am in the habit of writing one line per sentence because I typically compile things to LaTex, or am writing in some other format where line breaks get ignored. I use a blank line to indicate the ...
14
votes
7answers
2k views

How can I prepend a tag to the beginning of several files?

I need to add PHP tags surrounding a file. It's easy to append them using find . -exec echo "?>" >> '{}' \; but how can I prepend the tag <?php?
14
votes
6answers
7k views

Best way to follow a log and execute a command when some text appears in the log

I have a server log that outputs a specific line of text into its log file when the server is up. I want to execute a command once the server is up, and hence do something like the following: tail -f ...
14
votes
6answers
26k views

How to cut part from log file?

I have an 8 Gb log file (Rails production log). I need to cut it between some dates (lines). Which command could I use to do this?
13
votes
5answers
462 views

non-line-oriented tool for string replacement?

I recently asked a question about how to remove the newline character if it occurs after another specific character. Unix text-processing tools are very powerful, but almost all of them deal with ...
13
votes
6answers
24k views

How to convert TXT to PDF?

I want to convert .txt files to .pdf. I'm using this: ls | while read ONELINE; do convert -density 400 "$ONELINE" "$(echo "$ONELINE" | sed 's/.txt/.pdf/g')"; done But this produces one "error" -- ...
13
votes
8answers
3k views

Replace string containing newline in huge file

Anyone know of a non-line-based tool to "binary" search/replace strings in a somewhat memory-efficient way? See this question too. I have a +2GB text file that I would like to process similar to what ...
13
votes
2answers
6k views

Count how many times each line appears in a file

Say I have a file which contains: A A A B CC I want to have the output like this: A 3 B 1 CC 1