exstr(1)

exstr -- extract strings from source files

Synopsis

exstr file . . .

exstr -e file . . .

exstr -r [-d] file . . .

Description

The exstr utility is used to extract strings from C language source files and replace them by calls to the message retrieval function (see gettxt(3C)). This utility will extract all character strings surrounded by double quotes, not just strings used as arguments to the printf command or the printf routine. In the first form, exstr finds all strings in the source files and writes them on the standard output. Each string is preceded by the source file name and a colon. The meanings of the options are:

-e

Extract a list of strings from the named C language source files, with positional information. This list is produced on standard output in the following format:

file:line:position:msgfile:msgnum:string

The meanings of the fields are as follows:

file: the name of a C language source file
line: line number in the file
position: character position in the line
msgfile: null
msgnum: null
string: the extracted text string

Normally you would redirect this output into a file. Then you would edit this file to add the values you want to use for msgfile and msgnum:

msgfile: the file that contains the text strings that will replace string. A file with this name must be created and installed in the appropriate place by the mkmsgs(1) utility.
msgnum: the sequence number of the string in msgfile.

The next step is to use exstr -r to replace strings in file.

-r

Replace strings in a C language source file with function calls to the message retrieval function gettxt.

-d

This option is used together with the -r option. If the message retrieval fails when gettxt is invoked at run time, then the extracted string is printed.

You would use the capability provided by exstr on an application program that needs to run in an international environment and have messages print in more than one language. exstr replaces text strings with function calls that point at strings in a message database. The database used depends on the runtime value of the LC_MESSAGES environment variable (see environ(5)).

The first step is to use exstr -e to extract a list of strings and save it in a file. Next, examine this list and determine which strings can be translated and subsequently retrieved by the message retrieval function. Then, modify this file by deleting lines that can't be translated and, for lines that can be translated, by adding the message file names and the message numbers as the fourth (msgfile) and fifth (msgnum) entries on a line. The message files named must have been created by mkmsgs(1) and exist in /usr/lib/locale/locale/LC_MESSAGES. The directory locale corresponds to the language in which the text strings are written (see setlocale(3C)). The message numbers used must correspond to the sequence numbers of strings in the message files.

Now use this modified file as input to exstr -r to produce a new version of the original C language source file in which the strings have been replaced by calls to the message retrieval function gettxt. The msgfile and msgnum fields are used to construct the first argument to gettxt. The second argument to gettxt is printed if the message retrieval fails at run time. This argument is the null string, unless the -d option is used.

This utility cannot replace strings in all instances. For example, a static initialized character string cannot be replaced by a function call, or a string could be in the form of an escape sequence that cannot be translated. In order not to break existing code, the files created by invoking exstr -e must be examined and lines containing strings not replaceable by function calls must be deleted. In some cases the code may require modifications so that strings can be extracted and replaced by calls to the message retrieval function.

Examples

The following examples show uses of exstr.

Assume that the file foo.c contains two strings:

   main()
   {
   	printf("This is an example\n");
   	printf("Hello world!\n");
   }

The exstr utility, invoked with the argument foo.c, extracts strings from the named file and prints them on the standard output.

exstr foo.c produces the following output:

foo.c:This is an example\n
foo.c:Hello world!\n

exstr -e foo.c > foo.stringsout produces the following output in the file foo.stringsout:

foo.c:3:8:::This is an example\n
foo.c:4:8:::Hello world!\n

You must edit foo.stringsout to add the values you want to use for the msgfile and msgnum fields before these strings can be replaced by calls to the retrieval function. If UX is the name of the message file, and the numbers 1 and 2 represent the sequence number of the strings in the file, here is what foo.stringsout looks like after you add this information:

foo.c:3:8:UX:1:This is an example\n
foo.c:4:8:UX:2:Hello world!\n

The exstr utility can now be invoked with the -r option to replace the strings in the source file by calls to the message retrieval function gettxt.

exstr -r foo.c <foo.stringsout >intlfoo.c produces the following output:

   extern char gettxt();
   main()
   {
   	printf(gettxt("UX:1", ""));
   	printf(gettxt("UX:2", ""));
   }

exstr -rd foo.c <foo.stringsout >intlfoo.c uses the extracted strings as a second argument to gettxt.

   extern char gettxt();
   main()
   {
   	printf(gettxt("UX:1", "This is an example\n"));
   	printf(gettxt("UX:2", "Hello world!\n"));
   }

Files

/usr/lib/locale/locale/LC_MESSAGES/: files created by mkmsgs(1)

References

environ(5), fprintf(3S), gettxt(1), gettxt(3C), mkmsgs(1), printf(1), setlocale(3C), srchtxt(1)

Diagnostics

The error messages produced by exstr are intended to be self-explanatory. They indicate errors in the command line or format errors encountered within the input file.