.TL "" "" A Tour of the ast Commands and Libraries .AU "Glenn Fowler" gsf MH HA6163000 2195 2B-134 "[email protected]" .MT 4 .H 1 Introduction The .I ast commands and libraries were developed by the Software Engineering Research Department .RI ( aka the Advanced Software [Technology] Department) at AT&T Bell Laboratories, Murray Hill, NJ. The strength of .I ast is how its individual components combine to form a cohesive computing environment across UNIX\u\(rg\d and non-UNIX platforms. Cohesiveness* .FS Footnote test. .FE is maintained by well-defined library interfaces for algorithms upon which the commands are built. In many cases a library implementation was the driving force behind command implementations. .H 1 Motivation Why should you consider using the .I ast software? After all, many of the commands look like what's already in .L /bin and .LR /usr/local/gnu/bin . Although there is some replication, there are also some commands you won't find anywhere else: .I the ksh93, nmake, the 3d filesystem, cia, and yeast. .H 1 Installation The .I ast software installs in a single directory hierarchy, rooted at .LR $INSTALLROOT , usually .L /usr/local/ast or .LR /usr/add-on/ast . The top level .L $INSTALLROOT directories are: .EX bin executable binaries and scripts fun \fIksh93\fP shell functions lib libraries lib/\fIcommand\fP related files for \fIcommand\fP src/cmd/\fIxxx\fP source for command \fIxxx\fP src/lib/lib\fIxxx\fP source for library \fIxxx\fP .EE To access the commands and related data files: .EX export PATH=$INSTALLROOT/bin:$PATH .EE For each .I command that has a related data file .IR file , .I file is found by searching .L $PATH for .IL "" ../lib/ command / file , e.g., the magic file for the file command is .L ../lib/file/magic on .LR $PATH . If .L $HOME/bin is before .L $INSTALLROOT/bin in .L $PATH then you can selectively override standard .I ast related files by placing them in the directory .IL "" $HOME/lib/ command . This allows executables to be built without hard-coded pathnames and also requires only a change in .L $PATH when .L $INSTALLROOT changes. .P On systems with shared libraries one of .EX export LD_LIBRARY_PATH=$INSTALLROOT/lib:$LD_LIBRARY_PATH export LIBPATH=$INSTALLROOT/lib:$LIBPATH export LPATH=$INSTALLROOT/lib:$LPATH .EE is required to locate the .I ast shared libraries. .H 1 Exploration .I tw combines .I find and .IR xargs . It provides C style expressions on path names and elements of .LR "struct stat" . To find suspicious executables: .EX tw -d / -e "uid=='root' && (mode&'u+s') && parent.uid!=uid" .EE to change the owner of all of bozo's files: .EX tw -d / -e "uid=='bozo'" chown clown:circus .EE .I tw collects file pathname arguments up to the exec arg limit before it executes the command. For paranoid users: .EX tw chmod go-rwx .EE which is equivalent to: .EX chmod -R go-rwx .EE (Now you don't need to add a .L -R option to your favorite commands.) To find all source files that include .LR foo.h : .EX tw -e "name=='*.[chly]'" grep -l '^#.*include.*["<]foo\.h[>"]' .EE .P .I libast handles the magic number matching for the .I file command. The magic file, .LR $INSTALLROOT/lib/file/magic , is carefully constructed to give the same output across all architectures: .EX cd $HOME/arch file */bin/cat .EE might produce: .EX att.i386/bin/cat: elf i386 executable, 32-bit, little-endian, .. bsd.i386/bin/cat: bsd 386 executable, compact, paged, pure, no.. hp.pa/bin/cat: hp pa-risc executable, shared, dynamically l.. sgi.mips2/bin/cat: elf mips executable, 32-bit, dynamically lin.. sol.sun4/bin/cat: elf sparc executable, 32-bit, dynamically li.. sun4/bin/cat: sun sparc executable, paged, dynamically lin.. .EE .I tw uses the same interface, making it easy to search for files based on type, name and content. The following searches for executable scripts: .EX tw -e "(mode&'+x') && type!=DIR && magic!='*executable*'" .EE The .I tw algorithm efficiently detects file system loops, so following symbolic links is not a problem. The same algorithm is used by all .I ast commands that traverse directory hierarchies, and the following options to control pathname resolution: .EX -L (logical) follow symbolic links -P (physical) don't follow symbolic links -H (metaphysical) -L for command line files, -P otherwise .EE The .I ksh93 .I getconf builtin controls the default traversal mode: .EX getconf PATH_RESOLVE - { logical, physical, metaphysical } .EE .H 1 Configuration .H 1 Compression .H 1 Conclusion
