Software grep

If there is no response to an urgent issue, you can escalate to the general security mailing list for advice. Development of Grep, and GNU in general, is a volunteer effort, and you can contribute. For information, please read How to help GNU. If you'd like to get involved, it's a good idea to join the bug mailing list see above. We defend the rights of all software users. There are also other ways to contact the FSF. Portable scripts should avoid the following constructs, as POSIX says they produce undefined results:.

POSIX allows this behavior as an extension, but portable scripts should avoid it. See Environment Variables. In more-complex encodings such as UTF-8, a sequence of multiple bytes may be needed to represent a character, and some bytes may be encoding errors that do not contribute to the representation of any character.

POSIX does not specify the behavior of grep when patterns or input data contain encoding errors or null characters, so portable scripts should avoid such usage. In a regular expression, non-ASCII and non-printable characters other than newline are not special, and represent themselves.

Suppose you want to limit your pattern to only printable characters or even only printable ASCII characters to keep your script readable or portable, but you also want to match specific non-ASCII or non-null non-printable characters. However, none of these techniques will let you put a null character directly into a command-line pattern; null characters can appear only in a pattern specified via the -f --file option. This lists all lines in the files menu. See Regular Expressions.

Note that the regular expression syntax used in the pattern differs from the globbing syntax that the shell uses to match file names. See Invoking grep , for more details about how to invoke grep. For more control over which files are searched, use find and grep.

For example, the following command searches only C files:. The find command line above is more similar to the command:. For example:. If the pattern had been written without the square brackets, it would have matched not only the ps output line for cron , but also the ps output line for grep. Note that on some platforms, ps limits the output to the width of the screen; grep does not have any limit on the length of a line except the available memory.

So GNU grep suppresses output from files that appear to be binary files. To list the names of all files that contain no matching lines, use the -L or --files-without-match option. The grep command searches for lines that contain strings that match a pattern. Every line contains the empty string, so an empty pattern causes grep to find a match on each line. Standard grep cannot do this, as it is fundamentally line-based. Therefore, merely using the [:space:] character class does not match newlines in the way you might expect.

Thus, you can match newlines in the input, but typically if there is a match the entire input is output, so this usage is often combined with output-suppressing options like -q , e. If this does not suffice, you can transform the input before giving it to grep , or turn to awk , sed , perl , or many other utilities that are designed to operate across lines.

The name grep comes from the way line editing was done on Unix. For example, ed uses the following syntax to print a list of matching lines on the screen:. Typically grep is an efficient way to search text. However, it can be quite slow in some cases, and it can search large files where even minor performance tweaking can help significantly. Although the algorithm used by grep is an implementation detail that can change from release to release, understanding its basic strengths and weaknesses can help you improve its performance.

The grep command operates partly via a set of automata that are designed for efficiency, and partly via a slower matcher that takes over when the fast matchers run into unusual features like back-references. When feasible, the Boyer—Moore fast string searching algorithm is used to match a single fixed pattern, and the Aho—Corasick algorithm is used to match multiple fixed patterns. Generally speaking grep operates more efficiently in single-byte locales, since it can avoid the special processing needed for multi-byte characters.

On some operating systems that support files with holes—large regions of zeros that are not physically present on secondary storage— grep can skip over the holes efficiently without needing to read the zeros. For more about the algorithms used by grep and about related string matching algorithms, see:.

Bug reports can be found at the GNU bug report logs for grep. If you find a bug not listed there, please email it to bug-grep gnu. Up: Reporting bugs [ Contents ][ Index ]. In addition, certain other obscure regular expressions require exponential time and space, and may cause grep to run out of memory. Back-references can greatly slow down matching, as they can generate exponentially many matching possibilities that can consume both time and memory to explore.

Furthermore, many regular expression implementations have back-reference bugs that can cause programs to return incorrect answers or even crash, and fixing these bugs has often been low-priority: for example, as of the GNU C library bug database contained back-reference bugs 52 , , , and , with little sign of forthcoming fixes.

Luckily, back-references are rarely useful and it should be little trouble to avoid them in practical applications. In short, you have the right freedom to run and change grep and distribute it to other people, and—if you want—charge money for doing either.

The important restriction is that you have to grant your recipients the same rights and impose the same restrictions. This general method of licensing software is sometimes called open source. This manual is free documentation in the same sense. The documentation license is included below. Up: Copying [ Contents ][ Index ]. The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially.

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You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. But do not take my word for it! It really is an amazing, one-of-a-kind program. There is nothing to match it on any operating system. Every day I find some new amazing capability that makes it even more valuable.

Thank you for creating it, and also for the best documentation of RegEx to be found anywhere. Version 2. Operating Systems. Additional Requirements None. Total Downloads 36, Downloads Last Week Report Software. Related Software. Simple Sticky Notes Free. Take notes and stick them to your desktop.

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