Chapter 12

Redirection and Pipes

Figure 12.1  Standard files and file descriptors:(a) file descriptors(b) semantics of a command execution

Figure 12.2  Input redirection:(a) file descriptors and standard files for

‘command’(b) semantics of input redirection

Figure 12.3 Output redirection: (a) file descriptors and standard files for command’ (b) semantics of output redirection

Figure 12.3 Output redirection:(a) file descriptors and standard files for

‘command’(b) semantics of output redirection

Figure 12.4 Semantics of command run on remote server

rsh server sort < datafile

Figure 12.5  Combined use of input and output redirection

Figure 12.6  Error redirection:(a) file descriptors and standard files for

‘command’(b) semantics of error redirection

Figure 12.6  Error redirection:(a) file descriptors and standard files for

‘command’(b) semantics of error redirection

Figure 12.7  Error & Output redirection:cat lab1 lab2 lab3 1> cat.output 2> cat.errors

Figure 12.8 Error redirection:(a) file descriptors and standard files(b) semantics of the commands

cat lab1 lab2 lab3 1> cat.output.errors 2>&1 cat lab1 lab2 lab3 2> cat.output.errors 1>&2

Figure 12.8 Error redirection:(a) file descriptors and standard files(b) semantics of the commands

cat lab1 lab2 lab3 1> cat.output.errors 2>&1cat lab1 lab2 lab3 2> cat.output.errors 1>&2

Figure 12.9 Output and error redirection:(a) file descriptors and standard files for the cat command(b) standard files after cat lab1 lab2 lab3 2>&1

with no change in stdout and stderr(c) standard files after cat lab1 lab2 lab3 2>&1 1>

cat.output.errors(d) command semantics

Figure 12.9 Output and error redirection:(a) file descriptors and standard files for the cat command(b) standard files after cat lab1 lab2 lab3 2>&1

with no change in stdout and stderr(c) standard files after cat lab1 lab2 lab3 2>&1 1>

cat.output.errors(d) command semantics

Figure 12.10 Redirecting stdin, stdout, and stderr in a single command

Figure 12.11  The semantics of a pipeline with N commands

Figure 12.12  The semantics of the commandls -l | more command

Figure 12.13  The semantics of the commandgrep “John” < Students | lpr –Pspr

Figure 12.14  The semantics ofegrep ‘A$’ < ee446.grades | sort > ee446.As.sorted

Figure 12.15 The semantics of the commandrsh server cat ~/research/pvm/datafile.server | diff

datafile -

noclobber option

set -o noclobberDisables the overwriting of existing files

set +o noclobber• Disables the overwriting of existing files

tee Command

Syntaxtee [options] file-list

Reads input, echoes to stdin and all files in file-list

Figure 12.16  The semantics of the command cat names students | grep “John Doe” | tee file1

file2 | wc -l

Figure 12.17  Step-by-step semantics of the command

(find ~ -name foo -print > foo.paths) >& error.log

Figure 12.17  Step-by-step semantics of the command

(find ~ -name foo -print > foo.paths) >& error.log

Table 12.1 Redirection Operators and Their Meaning in Bash and TC Shells

Table 12.1 Redirection Operators and Their Meaning in Bash and TC Shells

Table 12.1 Redirection Operators and Their Meaning in Bash and TC Shells