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POBash-Scripting stderr and stdout
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2012-03-19T03:59:48.537
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2012-03-19T14:11:02.607
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2012-03-19T11:31:02.820
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I am new to bash-scripting & trying to understand how things work. It's all a bit strange.. I have two scripts. First this one: <pre><code>#!/usr/bin/bash #name: stderrtest0.sh echo "on ${1}: this is an error" >&2 echo "on ${1}: this is an info" >&1 echo "on ${1}: this is just text" </code></pre> And this second script calls the first: <pre><code>#!/usr/bin/bash #name: stderrtest1.sh echo "invoking: stderrtest0.sh test1 >&2 ~output:" ./stderrtest0.sh test1 >&2 echo "invoking: stderrtest0.sh test2 >&1 ~output:" ./stderrtest0.sh test2 >&1 echo "invoking: stderrtest0.sh test3 2>&1 ~output:" ./stderrtest0.sh test3 2>&1 echo "invoking: stderrtest0.sh test4 1>&2 ~output:" ./stderrtest0.sh test4 1>&2 echo "invoking: stderrtest0.sh test5 ~output:" ./stderrtest0.sh test5 </code></pre> Here are my tests (debian squeeze) with the output: METATEST1) invoke stderrtest1.sh <pre><code>$ ./stderrtest1.sh invoking: stderrtest0.sh test1 >&2 ~output: on test1: this is an error on test1: this is an info on test1: this is just text invoking: stderrtest0.sh test2 >&1 ~output: on test2: this is an error on test2: this is an info on test2: this is just text invoking: stderrtest0.sh test3 2>&1 ~output: on test3: this is an error on test3: this is an info on test3: this is just text invoking: stderrtest0.sh test4 1>&2 ~output: on test4: this is an error on test4: this is an info on test4: this is just text invoking: stderrtest0.sh test5 ~output: on test5: this is an error on test5: this is an info on test5: this is just text </code></pre> This is as I expect. Since by default <code>stderr</code> & <code>stdout</code> get sent to the terminal. METATEST2) invoke stderrtest1.sh & redirect output to out <pre><code>$ ./stderrtest1.sh >out on test1: this is an error on test1: this is an info on test1: this is just text on test2: this is an error on test4: this is an error on test4: this is an info on test4: this is just text on test5: this is an error $ cat out invoking: stderrtest0.sh test1 >&2 ~output: invoking: stderrtest0.sh test2 >&1 ~output: on test2: this is an info on test2: this is just text invoking: stderrtest0.sh test3 2>&1 ~output: on test3: this is an error on test3: this is an info on test3: this is just text invoking: stderrtest0.sh test4 1>&2 ~output: invoking: stderrtest0.sh test5 ~output: on test5: this is an info on test5: this is just text </code></pre> So here: <ul> <li>all <code>stdout</code> gets sent to the file out </li> <li>all <code>stderr</code> gets sent to the terminal</li> </ul> This is not quite as I expect. I somehow thought everything might end up in out METATEST3) invoke stderrtest1.sh & redirect <code>stdout</code> to inf.out <pre><code>$ ./stderrtest1.sh 1>inf.out on test1: this is an error on test1: this is an info on test1: this is just text on test2: this is an error on test4: this is an error on test4: this is an info on test4: this is just text on test5: this is an error $ cat inf.out invoking: stderrtest0.sh test1 >&2 ~output: invoking: stderrtest0.sh test2 >&1 ~output: on test2: this is an info on test2: this is just text invoking: stderrtest0.sh test3 2>&1 ~output: on test3: this is an error on test3: this is an info on test3: this is just text invoking: stderrtest0.sh test4 1>&2 ~output: invoking: stderrtest0.sh test5 ~output: on test5: this is an info on test5: this is just text </code></pre> Results are identical to METATEST2: <ul> <li>all <code>stdout</code> gets sent to the file inf.out</li> <li>all <code>stderr</code> gets sent to the terminal</li> </ul> Ok. Now I understand METATEST2. Redirecting without specification defaults to <code>stdout</code>. METATEST4) invoke stderrtest1.sh & redirect <code>stderr</code> to err.out <pre><code>$ ./stderrtest1.sh 2>err.out invoking: stderrtest0.sh test1 >&2 ~output: invoking: stderrtest0.sh test2 >&1 ~output: on test2: this is an info on test2: this is just text invoking: stderrtest0.sh test3 2>&1 ~output: on test3: this is an error on test3: this is an info on test3: this is just text invoking: stderrtest0.sh test4 1>&2 ~output: invoking: stderrtest0.sh test5 ~output: on test5: this is an info on test5: this is just text $ cat err.out on test1: this is an error on test1: this is an info on test1: this is just text on test2: this is an error on test4: this is an error on test4: this is an info on test4: this is just text on test5: this is an error </code></pre> And here I get confused. Because in METATEST3 test1: all output from stderrtest0.sh gets redirected to <code>stderr</code> & so goes to the terminal but not to inf.out And yet here in METATEST4 test2: all output from stderrtest1.sh is being redirected to <code>stdout</code> ~BUT the <code>stderr</code> emitted by stderrtest0.sh somehow escapes ? So this seems to imply: <ul> <li>any/all output from some called program can be redirected into the caller's <code>stderr</code>. </li> <li><code>stderr</code> output from some called program is not redirected into the caller's <code>stdout</code>.</li> </ul> Is this the case? 
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<bash><stdout><stderr>
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Bash-Scripting stderr and stdout
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