strings - find printable strings in files
strings [-a] [-t format] [-n number] [file...]
The strings utility shall look for printable strings in regular files and shall write those strings to standard output. A printable string is any sequence of four (by default) or more printable characters terminated by a <newline> or NUL character. Additional implementation-defined strings may be written; see localedef.
If the first argument is '-', the results are unspecified.
The strings utility shall conform to XBD Utility Syntax Guidelines, except for the unspecified usage of '-'.
The following options shall be supported:
- Scan files in their entirety. If -a is not specified, it is implementation-defined what portion of each file is scanned for strings.
- -n number
- Specify the minimum string length, where the number argument is a positive decimal integer. The default shall be 4.
- -t format
- Write each string preceded by its byte offset from the start of the file. The format shall be dependent on the single character used as the format option-argument:
- The offset shall be written in decimal.
- The offset shall be written in octal.
- The offset shall be written in hexadecimal.
The following operand shall be supported:
- A pathname of a regular file to be used as input. If no file operand is specified, the strings utility shall read from the standard input.
See the INPUT FILES section.
The input files named by the utility arguments or the standard input shall be regular files of any format.
The following environment variables shall affect the execution of strings:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files) and to identify printable strings.
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
Strings found shall be written to the standard output, one per line.
When the -t option is not specified, the format of the output shall be:"%s", <string>
With the -t o option, the format of the output shall be:"%o %s", <byte offset>, <string>
With the -t x option, the format of the output shall be:"%x %s", <byte offset>, <string>
With the -t d option, the format of the output shall be:"%d %s", <byte offset>, <string>
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion.
- An error occurred.
By default the data area (as opposed to the text, "bss", or header areas) of a binary executable file is scanned. Implementations document which areas are scanned.
Some historical implementations do not require NUL or <newline> terminators for strings to permit those languages that do not use NUL as a string terminator to have their strings written.
Apart from rationalizing the option syntax and slight difficulties with object and executable binary files, strings is specified to match historical practice closely. The -a and -n options were introduced to replace the non-conforming - and - number options. These options are no longer specified by POSIX.1-2017 but may be present in some implementations.
The -o option historically means different things on different implementations. Some use it to mean " offset in decimal", while others use it as " offset in octal". Instead of trying to decide which way would be least objectionable, the -t option was added. It was originally named -O to mean "offset", but was changed to -t to be consistent with od.
The ISO C standard function isprint() is restricted to a domain of unsigned char. This volume of POSIX.1-2017 requires implementations to write strings as defined by the current locale.
XBD Environment Variables, Utility Syntax Guidelines
First released in Issue 4.
This utility is marked as part of the User Portability Utilities option.
The obsolescent SYNOPSIS is removed.
The normative text is reworded to avoid use of the term "must" for application requirements.
Austin Group Interpretation 1003.1-2001 #027 is applied, clarifying the behavior if the first argument is '-'.
The strings utility is moved from the User Portability Utilities option to the Base. User Portability Utilities is now an option for interactive utilities.
SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.
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