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authorWes Turner <wes.turner@gmail.com>2014-10-30 19:20:05 -0500
committerWes Turner <wes@wrd.nu>2014-11-01 12:22:45 -0500
commite287075690f73c934825fc413bcc4a3e2be4456d (patch)
treee8413329c0aeaeaf64f40b4d40cedda6eb569b7b /bash.html.markdown
parent02e81acfe1dc548553082672a2d04f826a0812e6 (diff)
[bash/en] bash.html.markdown: add bash redirection examples
Diffstat (limited to 'bash.html.markdown')
-rw-r--r--bash.html.markdown45
1 files changed, 39 insertions, 6 deletions
diff --git a/bash.html.markdown b/bash.html.markdown
index 11c1f3a2..b0011420 100644
--- a/bash.html.markdown
+++ b/bash.html.markdown
@@ -111,12 +111,45 @@ ls -l # Lists every file and directory on a separate line
# .txt files in the current directory:
ls -l | grep "\.txt"
-# You can also redirect a command, input and error output.
-python2 hello.py < "input.in"
-python2 hello.py > "output.out"
-python2 hello.py 2> "error.err"
-# The output error will overwrite the file if it exists, if you want to
-# concatenate them, use ">>" instead.
+# You can redirect command input and output (stdin, stdout, and stderr).
+# Read from stdin until ^EOF$ and overwrite hello.py with the lines
+# between "EOF":
+cat > hello.py << EOF
+#!/usr/bin/env python
+from __future__ import print_function
+import sys
+print("#stdout", file=sys.stdout)
+print("#stderr", file=sys.stderr)
+for line in sys.stdin:
+ print(line, file=sys.stdout)
+EOF
+
+# Run hello.py with various stdin, stdout, and stderr redirections:
+python hello.py < "input.in"
+python hello.py > "output.out"
+python hello.py 2> "error.err"
+python hello.py > "output-and-error.log" 2>&1
+python hello.py > /dev/null 2>&1
+# The output error will overwrite the file if it exists,
+# if you want to append instead, use ">>":
+python hello.py >> "output.out" 2>> "error.err"
+
+# Overwrite output.txt, append to error.err, and count lines:
+info bash 'Basic Shell Features' 'Redirections' > output.out 2>> error.err
+wc -l output.out error.err
+
+# Run a command and print its file descriptor (e.g. /dev/fd/123)
+# see: man fd
+echo <(echo "#helloworld")
+
+# Overwrite output.txt with "#helloworld":
+cat > output.out <(echo "#helloworld")
+echo "#helloworld" > output.out
+echo "#helloworld" | cat > output.out
+echo "#helloworld" | tee output.out >/dev/null
+
+# Cleanup temporary files verbosely (add '-i' for interactive)
+rm -v output.out error.err output-and-error.log
# Commands can be substituted within other commands using $( ):
# The following command displays the number of files and directories in the