52 lines
2.1 KiB
Sed
52 lines
2.1 KiB
Sed
# Fixed environment access and mutation using regular expressions
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#
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# Copyright (C) 2018 Mike Gerwitz
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# This is a fairly simply example demonstrating how an environment
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# consisting of pre-determined variables can be accessed and manipulated
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# using only regular expressions (in the formal sense).
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#
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# See also `env-dyn.sed' for a a much more sophisticated example of a
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# dynamic environment where the variables are _not_ pre-determined.
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##
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# Read all lines into the pattern space.
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:a; N; $!ba
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# Variable reference in an assignment form. This copies the value from the
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# environment line into the assignment line. Note that this will only
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# perform a single replacement per variable. Because regexes are greedy,
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# this will replace the _last_ occurrence in the assignment form with the
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# value of the current environment.
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s/\(x=\)\([^ ]*\)\(.*\n.<-.*\)x/\1\2\3\2/
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s/\(y=\)\([^ ]*\)\(.*\n.<-.*\)y/\1\2\3\2/
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s/\(z=\)\([^ ]*\)\(.*\n.<-.*\)z/\1\2\3\2/
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# Environment mutation. This assigns a new value to the environment by
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# copying the value from the assignment line into the environment line.
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s/\(x=\)[^ ]*\(.*\)\nx<-\([^ ]*\)/\1\3\2/
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s/\(y=\)[^ ]*\(.*\)\ny<-\([^ ]*\)/\1\3\2/
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s/\(z=\)[^ ]*\(.*\)\nz<-\([^ ]*\)/\1\3\2/
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# The above expressions should have eliminated the assignment line if there
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# was a match; if it still exists, then there is a syntax error.
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s/.<-.*$/ERROR: &/
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# This script only handles a single pass. Let the animate script know that
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# we are done.
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q1
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