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Questions tagged [variable-expansion]

Evaluating or expanding a variable to get its value. Depending on the language, a variable may be expanded one or more times.

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Why does GNU Make re-run my shell command every time it expands this variable?

I use OpenSSL to generate some random data in a GNU Makefile: RANDOM_DATA=$(shell /usr/bin/openssl rand -hex 32) I want to be able to use this RANDOM_DATA multiple times elsewhere in the script. However, every time it's referenced, it re-runs the…
Steve
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Zsh does not expand path in `--flag=path` style arguments

In bash: $ foo --bar=/tmp/ba expands to foo --bar/tmp/baz. In my zsh install, no expansion is performed here (but is performed as expected when the path is separated by whitespace, i.e. foo --bar /tmp/ba). What zsh setting do I need to…
Sasgorilla
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Bash array variable expansion inside expect command

An extension to this question : Bash : Adding extra single quotes to strings with spaces After storing the arguments of command as a bash array touch "some file.txt" file="some file.txt" # Create an array with two elements; the second element…
anoop.babu
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Can Java Streams transform a list of points into a list of their coordinates?

I have a stream of Point3Ds in a JavaFX 8 program. I would like, for the sake of creating a Mesh from them, to be able to produce a list of their (x, y, z) coordinates instead. This is a simple enough task through traditional Java looping. (Almost…
Michael Macha
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GNU Make: How to perform second expansion with suffix-changing substitution

What I'm going for (what's failing) I have a list of dependencies for each file: point_deps = bounds_deps = point triangle_deps = point bounds Image_deps = types bounds triangle main_deps = Image triangle bounds point types I'd like to write a rule…
joshterrell805
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What does the POSIX spec mean when it says this is necessary to avoid ambiguity?

When responding to this comment: Now I got the the two ":"s are independent, and that's why I couldn't find any document about them. Is the first one needed in this case? I noticed this paragraph in the spec for the first time: In the parameter…
Etan Reisner
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removing a case clause: bash expansion in sed regexp: X='a\.b' ; Y=';;' sed -n '/${X}/,/${Y}/d'

I'm trying to remove a case clause from a bash script. The clause will vary, but will always have backslashes as part of the case-match string. I was trying sed but could use awk or a perl one-liner within the bash script. The target of the edit is…
ChrisSM
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Shell splitting in subshell

I have unclear information about word splitting in Shell and subshells. Example: IFS="" file_name="file with space" file_name=$(real_path $file_name) Will $file_name get split in subshell? Or do I have to double-quote it like…
semtexzv
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shell :How to use UDV in this Grep structure without having issues?

I have an assigment that asks me to print on screen the number of words that are longer than a given number ,let's say k , which is read from the keyboard. and then to order the result. Until now I decided to try in this way : #!bin/bash k=0 if […
Wiuwi
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zsh redirection, together with parameter expansion

I'm writing a shell script S which calls a program P. P accepts its input from stdin only. One of the parameters of my script S is optional; if the parameter is present, it denotes a file, which should be fed into P. If the parameter is missing,…
user1934428
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Either getting original return value from xargs or simulate xargs

I am working with bash. I have a file F containing the command-line arguments for a Java program, and I need to store both outputs of the Java programs, i.e., output on standard output and the exit value. Storing the standard output works via cat F…
Oliver Kullmann
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Using quotes with "${parameter:-word}" Parameter Expansion

When using the ${parameter:-word} form of parameter expansion to evaluate to a default value if the variable is unset, what is the best practice for quotes? For example, assume a Bash shell script with -u set (to generate an error when an undefined…
jetset
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Bash - Command and variable expansion

After reading the POSIX Shell manual and the Bash manual I still can't explain the following behavior: % bash --version GNU bash, version 3.2.48(1)-release (x86_64-unknown-linux-gnu) Copyright (C) 2007 Free Software Foundation, Inc. % bash % A=1…
A. Lefebvre
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Replace variables in text: Suggestions?

I'm looking for a nice template engine or short piece of code to expand Ant-like variables in a string in Java. Example: String result = expand ("${firstName} ${familyName}", map); It should at least support java.util.Map but something that can…
Aaron Digulla
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How does ipython variable expansion works?

I don't understand what the ${} is doing in the fourth and sixth prompt, and I can't find any documentation about this, The book Python for Unix and Linux System Administrator has an example like the one in the sixth prompt, in which the variable is…
HarmonicaMuse
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