linux PATH环境变量 中 相同变量名的调用优先级

测试 使用plink v1.07 和 plink v1.9两个软件版本进行测试

001、将plink v1.07 的变量放在 plink v1.9之前， 观测系统调用的plink版本

[liujiaxin01@PC1 ~]$ echo $PATH     ## 输出当前的PATH变量
/home/liujiaxin01/anaconda3/condabin:/home/liujiaxin01/.local/bin:/home/liujiaxin01/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/software/gatk-4.1.9.0:/home/software/picard
[liujiaxin01@PC1 ~]$ PATH=/home/liujiaxin01/anaconda3/condabin:/home/liujiaxin01/.local/bin:/home/liujiaxin01/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/software/gatk-4.1.9.0:/home/software/picard:/home/liujiaxin01/software/plink17:/home/liujiaxin01/software/plink19
[liujiaxin01@PC1 ~]$ plink         ## 将plink1.07变量放在plink1.9之前， 调用plink测试， 发现调用起来的是plink v1.07

@----------------------------------------------------------@
|        PLINK!       |     v1.07      |   10/Aug/2009     |
|----------------------------------------------------------|
|  (C) 2009 Shaun Purcell, GNU General Public License, v2  |
|----------------------------------------------------------|
|  For documentation, citation & bug-report instructions:  |
|        http://pngu.mgh.harvard.edu/purcell/plink/        |
@----------------------------------------------------------@

Web-based version check ( --noweb to skip )
Connecting to web... ^C

002、调换 plinkv1.07和plink1.9的顺序， 即plinkv1.9变量放在plinkv1.07之前，观察系统调用的优先级

[liujiaxin01@PC1 ~]$ echo $PATH       ## 输出当前的PATH变量内容
/home/liujiaxin01/anaconda3/condabin:/home/liujiaxin01/.local/bin:/home/liujiaxin01/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/software/gatk-4.1.9.0:/home/software/picard:/home/liujiaxin01/software/plink17:/home/liujiaxin01/software/plink19
[liujiaxin01@PC1 ~]$ PATH=/home/liujiaxin01/anaconda3/condabin:/home/liujiaxin01/.local/bin:/home/liujiaxin01/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/software/gatk-4.1.9.0:/home/software/picard:/home/liujiaxin01/software/plink19:/home/liujiaxin01/software/plink17
[liujiaxin01@PC1 ~]$ echo $PATH        ## 将变量plinkv1.9 放在plinkv1.07之前， 并输出PATH变量     
/home/liujiaxin01/anaconda3/condabin:/home/liujiaxin01/.local/bin:/home/liujiaxin01/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/software/gatk-4.1.9.0:/home/software/picard:/home/liujiaxin01/software/plink19:/home/liujiaxin01/software/plink17
[liujiaxin01@PC1 ~]$ plink          ## 测试系统调用的优先级， 调用plinv1.9
PLINK v1.90b6.27 64-bit (10 Dec 2022)          www.cog-genomics.org/plink/1.9/
(C) 2005-2022 Shaun Purcell, Christopher Chang   GNU General Public License v3

  plink <input flag(s)...> [command flag(s)...] [other flag(s)...]
  plink --help [flag name(s)...]

Commands include --make-bed, --recode, --flip-scan, --merge-list,
--write-snplist, --list-duplicate-vars, --freqx, --missing, --test-mishap,
--hardy, --mendel, --ibc, --impute-sex, --indep-pairphase, --r2, --show-tags,
--blocks, --distance, --genome, --homozyg, --make-rel, --make-grm-gz,
--rel-cutoff, --cluster, --pca, --neighbour, --ibs-test, --regress-distance,
--model, --bd, --gxe, --logistic, --dosage, --lasso, --test-missing,
--make-perm-pheno, --tdt, --qfam, --annotate, --clump, --gene-report,
--meta-analysis, --epistasis, --fast-epistasis, and --score.

"plink --help | more" describes all functions (warning: long).

小结：当PATH环境变量中存在相同的变量名时， 系统优先调用PATH变量名中最前面的那个变量。